diff --git a/Tests/Perspex.Markup.Xaml.UnitTests/DataContextChangeSynchronizerTest.cs b/Tests/Perspex.Markup.Xaml.UnitTests/DataContextChangeSynchronizerTest.cs
index f2f3d949a6..0b93a2421d 100644
--- a/Tests/Perspex.Markup.Xaml.UnitTests/DataContextChangeSynchronizerTest.cs
+++ b/Tests/Perspex.Markup.Xaml.UnitTests/DataContextChangeSynchronizerTest.cs
@@ -16,9 +16,9 @@ namespace Perspex.Xaml.Base.UnitTest
 {
     public class DataContextChangeSynchronizerTest
     {
-        private TypeConverterProvider _repo;
-        private SamplePerspexObject _guiObject;
-        private ViewModelMock _viewModel;
+        private readonly TypeConverterProvider _repo;
+        private readonly SamplePerspexObject _guiObject;
+        private readonly ViewModelMock _viewModel;
 
         public DataContextChangeSynchronizerTest()
         {
diff --git a/samples/TestApplication/Program.cs b/samples/TestApplication/Program.cs
index d4e7232a62..de07b8d692 100644
--- a/samples/TestApplication/Program.cs
+++ b/samples/TestApplication/Program.cs
@@ -40,7 +40,7 @@ namespace TestApplication
 
     internal class Program
     {
-        private static PerspexList<Node> s_treeData = new PerspexList<Node>
+        private static readonly PerspexList<Node> s_treeData = new PerspexList<Node>
         {
             new Node
             {
@@ -78,7 +78,7 @@ namespace TestApplication
             },
         };
 
-        private static PerspexList<Item> s_listBoxData = new PerspexList<Item>
+        private static readonly PerspexList<Item> s_listBoxData = new PerspexList<Item>
         {
             new Item { Name = "Item 1", Value = "Item 1 Value" },
             new Item { Name = "Item 2", Value = "Item 2 Value" },
diff --git a/src/Gtk/Perspex.Cairo/CairoPlatform.cs b/src/Gtk/Perspex.Cairo/CairoPlatform.cs
index 1d23cb9135..b6d14e60a1 100644
--- a/src/Gtk/Perspex.Cairo/CairoPlatform.cs
+++ b/src/Gtk/Perspex.Cairo/CairoPlatform.cs
@@ -14,7 +14,7 @@ namespace Perspex.Cairo
 
     public class CairoPlatform : IPlatformRenderInterface
     {
-        private static CairoPlatform s_instance = new CairoPlatform();
+        private static readonly CairoPlatform s_instance = new CairoPlatform();
 
         public static void Initialize()
         {
diff --git a/src/Gtk/Perspex.Cairo/Media/DrawingContext.cs b/src/Gtk/Perspex.Cairo/Media/DrawingContext.cs
index e64ab60fb5..5fc767ef57 100644
--- a/src/Gtk/Perspex.Cairo/Media/DrawingContext.cs
+++ b/src/Gtk/Perspex.Cairo/Media/DrawingContext.cs
@@ -19,7 +19,7 @@ namespace Perspex.Cairo.Media
         /// <summary>
         /// The cairo context.
         /// </summary>
-        private Cairo.Context _context;
+        private readonly Cairo.Context _context;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DrawingContext"/> class.
diff --git a/src/Gtk/Perspex.Cairo/Media/StreamGeometryContextImpl.cs b/src/Gtk/Perspex.Cairo/Media/StreamGeometryContextImpl.cs
index 5da6a0cf21..47a822865d 100644
--- a/src/Gtk/Perspex.Cairo/Media/StreamGeometryContextImpl.cs
+++ b/src/Gtk/Perspex.Cairo/Media/StreamGeometryContextImpl.cs
@@ -12,7 +12,7 @@ namespace Perspex.Cairo.Media
 
     public class StreamGeometryContextImpl : IStreamGeometryContextImpl
     {
-        private StreamGeometryImpl _impl;
+        private readonly StreamGeometryImpl _impl;
         public StreamGeometryContextImpl(StreamGeometryImpl imp)
         {
             _impl = imp;
@@ -39,8 +39,8 @@ namespace Perspex.Cairo.Media
             _context.LineTo(point.ToCairo());
         }
 
-        private Cairo.Context _context;
-        private Cairo.ImageSurface _surf;
+        private readonly Cairo.Context _context;
+        private readonly Cairo.ImageSurface _surf;
 
         public void EndFigure(bool isClosed)
         {
diff --git a/src/Gtk/Perspex.Cairo/Media/StreamGeometryImpl.cs b/src/Gtk/Perspex.Cairo/Media/StreamGeometryImpl.cs
index 8af8fd586e..a87c1b06e2 100644
--- a/src/Gtk/Perspex.Cairo/Media/StreamGeometryImpl.cs
+++ b/src/Gtk/Perspex.Cairo/Media/StreamGeometryImpl.cs
@@ -36,7 +36,7 @@ namespace Perspex.Cairo.Media
             set;
         }
 
-        private StreamGeometryContextImpl _impl;
+        private readonly StreamGeometryContextImpl _impl;
 
         private Matrix _transform = Matrix.Identity;
         public Matrix Transform
diff --git a/src/Gtk/Perspex.Cairo/Renderer.cs b/src/Gtk/Perspex.Cairo/Renderer.cs
index 1959eb940e..9454ce4bea 100644
--- a/src/Gtk/Perspex.Cairo/Renderer.cs
+++ b/src/Gtk/Perspex.Cairo/Renderer.cs
@@ -17,7 +17,7 @@ namespace Perspex.Cairo
     /// </summary>
     public class Renderer : RendererBase
     {
-        private Surface _surface;
+        private readonly Surface _surface;
         private Gdk.Window _window;
 
         /// <summary>
diff --git a/src/Gtk/Perspex.Gtk/GtkPlatform.cs b/src/Gtk/Perspex.Gtk/GtkPlatform.cs
index 1e5b9a5f14..d02e112845 100644
--- a/src/Gtk/Perspex.Gtk/GtkPlatform.cs
+++ b/src/Gtk/Perspex.Gtk/GtkPlatform.cs
@@ -14,7 +14,7 @@ namespace Perspex.Gtk
 
     public class GtkPlatform : IPlatformThreadingInterface, IPlatformSettings
     {
-        private static GtkPlatform s_instance = new GtkPlatform();
+        private static readonly GtkPlatform s_instance = new GtkPlatform();
 
         public GtkPlatform()
         {
diff --git a/src/Gtk/Perspex.Gtk/Input/GtkKeyboardDevice.cs b/src/Gtk/Perspex.Gtk/Input/GtkKeyboardDevice.cs
index 5dcf4af138..4fdd54a2b2 100644
--- a/src/Gtk/Perspex.Gtk/Input/GtkKeyboardDevice.cs
+++ b/src/Gtk/Perspex.Gtk/Input/GtkKeyboardDevice.cs
@@ -10,7 +10,7 @@ namespace Perspex.Gtk
 {
     public class GtkKeyboardDevice : KeyboardDevice
     {
-        private static GtkKeyboardDevice s_instance;
+        private static readonly GtkKeyboardDevice s_instance;
         private static readonly Dictionary<Gdk.Key, string> NameDic = new Dictionary<Gdk.Key, string>();
 
         static GtkKeyboardDevice()
diff --git a/src/Gtk/Perspex.Gtk/Input/GtkMouseDevice.cs b/src/Gtk/Perspex.Gtk/Input/GtkMouseDevice.cs
index 3436ada8d7..055421a04a 100644
--- a/src/Gtk/Perspex.Gtk/Input/GtkMouseDevice.cs
+++ b/src/Gtk/Perspex.Gtk/Input/GtkMouseDevice.cs
@@ -6,7 +6,7 @@ namespace Perspex.Gtk
 {
     public class GtkMouseDevice : MouseDevice
     {
-        private static GtkMouseDevice s_instance;
+        private static readonly GtkMouseDevice s_instance;
 
         private Point _clientPosition;
 
diff --git a/src/Markup/Perspex.Markup.Xaml/DataBinding/XamlBindingDefinition.cs b/src/Markup/Perspex.Markup.Xaml/DataBinding/XamlBindingDefinition.cs
index 7851a0cb95..cce86455d6 100644
--- a/src/Markup/Perspex.Markup.Xaml/DataBinding/XamlBindingDefinition.cs
+++ b/src/Markup/Perspex.Markup.Xaml/DataBinding/XamlBindingDefinition.cs
@@ -8,8 +8,8 @@ namespace Perspex.Markup.Xaml.DataBinding
 {
     public class XamlBindingDefinition
     {
-        private PropertyPath _sourcePropertyPath;
-        private BindingMode _bindingMode;
+        private readonly PropertyPath _sourcePropertyPath;
+        private readonly BindingMode _bindingMode;
         private readonly Control _target;
         private readonly PerspexProperty _targetProperty;
 
diff --git a/src/Perspex.Animation/Animation.cs b/src/Perspex.Animation/Animation.cs
index 60c05bde2e..26e839e154 100644
--- a/src/Perspex.Animation/Animation.cs
+++ b/src/Perspex.Animation/Animation.cs
@@ -13,12 +13,12 @@ namespace Perspex.Animation
         /// <summary>
         /// The animation being tracked.
         /// </summary>
-        private IObservable<object> _inner;
+        private readonly IObservable<object> _inner;
 
         /// <summary>
         /// The disposable used to cancel the animation.
         /// </summary>
-        private IDisposable _subscription;
+        private readonly IDisposable _subscription;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Animation"/> class.
diff --git a/src/Perspex.Animation/Animation`1.cs b/src/Perspex.Animation/Animation`1.cs
index 9f6d2a9498..be04a5a33d 100644
--- a/src/Perspex.Animation/Animation`1.cs
+++ b/src/Perspex.Animation/Animation`1.cs
@@ -14,12 +14,12 @@ namespace Perspex.Animation
         /// <summary>
         /// The animation being tracked.
         /// </summary>
-        private IObservable<T> _inner;
+        private readonly IObservable<T> _inner;
 
         /// <summary>
         /// The disposable used to cancel the animation.
         /// </summary>
-        private IDisposable _subscription;
+        private readonly IDisposable _subscription;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Animation{T}"/> class.
diff --git a/src/Perspex.Application/Application.cs b/src/Perspex.Application/Application.cs
index 9555db5bfa..09ab0a892a 100644
--- a/src/Perspex.Application/Application.cs
+++ b/src/Perspex.Application/Application.cs
@@ -45,7 +45,7 @@ namespace Perspex
         /// <summary>
         /// The styler that will be used to apply styles to controls.
         /// </summary>
-        private Styler _styler = new Styler();
+        private readonly Styler _styler = new Styler();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Application"/> class.
diff --git a/src/Perspex.Base/PerspexObject.cs b/src/Perspex.Base/PerspexObject.cs
index 748901f1bf..3763326577 100644
--- a/src/Perspex.Base/PerspexObject.cs
+++ b/src/Perspex.Base/PerspexObject.cs
@@ -68,7 +68,7 @@ namespace Perspex
         /// <summary>
         /// The registered properties by type.
         /// </summary>
-        private static Dictionary<Type, List<PerspexProperty>> s_registered =
+        private static readonly Dictionary<Type, List<PerspexProperty>> s_registered =
             new Dictionary<Type, List<PerspexProperty>>();
 
         /// <summary>
@@ -79,7 +79,7 @@ namespace Perspex
         /// <summary>
         /// The set values/bindings on this object.
         /// </summary>
-        private Dictionary<PerspexProperty, PriorityValue> _values =
+        private readonly Dictionary<PerspexProperty, PriorityValue> _values =
             new Dictionary<PerspexProperty, PriorityValue>();
 
         /// <summary>
@@ -90,7 +90,7 @@ namespace Perspex
         /// <summary>
         /// A serilog logger for logging property events.
         /// </summary>
-        private ILogger _propertyLog;
+        private readonly ILogger _propertyLog;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PerspexObject"/> class.
diff --git a/src/Perspex.Base/PerspexProperty.cs b/src/Perspex.Base/PerspexProperty.cs
index a6e8bf7b0d..20bacdb4e9 100644
--- a/src/Perspex.Base/PerspexProperty.cs
+++ b/src/Perspex.Base/PerspexProperty.cs
@@ -25,22 +25,22 @@ namespace Perspex
         /// <summary>
         /// The default values for the property, by type.
         /// </summary>
-        private Dictionary<Type, object> _defaultValues = new Dictionary<Type, object>();
+        private readonly Dictionary<Type, object> _defaultValues = new Dictionary<Type, object>();
 
         /// <summary>
         /// Observable fired when this property changes on any <see cref="PerspexObject"/>.
         /// </summary>
-        private Subject<PerspexPropertyChangedEventArgs> _initialized = new Subject<PerspexPropertyChangedEventArgs>();
+        private readonly Subject<PerspexPropertyChangedEventArgs> _initialized = new Subject<PerspexPropertyChangedEventArgs>();
 
         /// <summary>
         /// Observable fired when this property changes on any <see cref="PerspexObject"/>.
         /// </summary>
-        private Subject<PerspexPropertyChangedEventArgs> _changed = new Subject<PerspexPropertyChangedEventArgs>();
+        private readonly Subject<PerspexPropertyChangedEventArgs> _changed = new Subject<PerspexPropertyChangedEventArgs>();
 
         /// <summary>
         /// The validation functions for the property, by type.
         /// </summary>
-        private Dictionary<Type, Func<PerspexObject, object, object>> _validation =
+        private readonly Dictionary<Type, Func<PerspexObject, object, object>> _validation =
             new Dictionary<Type, Func<PerspexObject, object, object>>();
 
         /// <summary>
diff --git a/src/Perspex.Base/PriorityLevel.cs b/src/Perspex.Base/PriorityLevel.cs
index 2d22526e4a..b7ffcce971 100644
--- a/src/Perspex.Base/PriorityLevel.cs
+++ b/src/Perspex.Base/PriorityLevel.cs
@@ -50,7 +50,7 @@ namespace Perspex
         /// <summary>
         /// Method called when current value changes.
         /// </summary>
-        private Action<PriorityLevel> _changed;
+        private readonly Action<PriorityLevel> _changed;
 
         /// <summary>
         /// The current direct value.
@@ -62,7 +62,7 @@ namespace Perspex
         /// </summary>
         private int _nextIndex;
 
-        private LevelPrecedenceMode _mode;
+        private readonly LevelPrecedenceMode _mode;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PriorityLevel"/> class.
diff --git a/src/Perspex.Base/PriorityValue.cs b/src/Perspex.Base/PriorityValue.cs
index 0764a912c5..4be6b88861 100644
--- a/src/Perspex.Base/PriorityValue.cs
+++ b/src/Perspex.Base/PriorityValue.cs
@@ -27,22 +27,22 @@ namespace Perspex
         /// <summary>
         /// The name of the property.
         /// </summary>
-        private string _name;
+        private readonly string _name;
 
         /// <summary>
         /// The value type.
         /// </summary>
-        private Type _valueType;
+        private readonly Type _valueType;
 
         /// <summary>
         /// The currently registered bindings organised by priority.
         /// </summary>
-        private Dictionary<int, PriorityLevel> _levels = new Dictionary<int, PriorityLevel>();
+        private readonly Dictionary<int, PriorityLevel> _levels = new Dictionary<int, PriorityLevel>();
 
         /// <summary>
         /// The changed observable.
         /// </summary>
-        private Subject<Tuple<object, object>> _changed = new Subject<Tuple<object, object>>();
+        private readonly Subject<Tuple<object, object>> _changed = new Subject<Tuple<object, object>>();
 
         /// <summary>
         /// The current value.
@@ -52,7 +52,7 @@ namespace Perspex
         /// <summary>
         /// The function used to validate the value, if any.
         /// </summary>
-        private Func<object, object> _validate;
+        private readonly Func<object, object> _validate;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PriorityValue"/> class.
diff --git a/src/Perspex.Base/Threading/Dispatcher.cs b/src/Perspex.Base/Threading/Dispatcher.cs
index 60af8611f0..629492c2d0 100644
--- a/src/Perspex.Base/Threading/Dispatcher.cs
+++ b/src/Perspex.Base/Threading/Dispatcher.cs
@@ -17,9 +17,9 @@ namespace Perspex.Threading
     /// </remarks>
     public class Dispatcher
     {
-        private static Dispatcher s_instance = new Dispatcher();
+        private static readonly Dispatcher s_instance = new Dispatcher();
 
-        private MainLoop _mainLoop = new MainLoop();
+        private readonly MainLoop _mainLoop = new MainLoop();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Dispatcher"/> class.
diff --git a/src/Perspex.Base/Threading/DispatcherTimer.cs b/src/Perspex.Base/Threading/DispatcherTimer.cs
index bbb6f61031..21c3da0f8d 100644
--- a/src/Perspex.Base/Threading/DispatcherTimer.cs
+++ b/src/Perspex.Base/Threading/DispatcherTimer.cs
@@ -15,7 +15,7 @@ namespace Perspex.Threading
     {
         private IDisposable _timer;
 
-        private DispatcherPriority _priority;
+        private readonly DispatcherPriority _priority;
 
         private TimeSpan _interval;
 
diff --git a/src/Perspex.Base/Threading/MainLoop.cs b/src/Perspex.Base/Threading/MainLoop.cs
index 0fe3cbece9..b657fc04a2 100644
--- a/src/Perspex.Base/Threading/MainLoop.cs
+++ b/src/Perspex.Base/Threading/MainLoop.cs
@@ -16,9 +16,9 @@ namespace Perspex.Win32.Threading
     /// </summary>
     internal class MainLoop
     {
-        private static IPlatformThreadingInterface s_platform;
+        private static readonly IPlatformThreadingInterface s_platform;
 
-        private PriorityQueue<Job, DispatcherPriority> _queue =
+        private readonly PriorityQueue<Job, DispatcherPriority> _queue =
             new PriorityQueue<Job, DispatcherPriority>(PriorityQueueType.Maximum);
 
         /// <summary>
diff --git a/src/Perspex.Controls/Control.cs b/src/Perspex.Controls/Control.cs
index c7f7afa221..12ae649f91 100644
--- a/src/Perspex.Controls/Control.cs
+++ b/src/Perspex.Controls/Control.cs
@@ -67,7 +67,7 @@ namespace Perspex.Controls
         public static readonly RoutedEvent<RequestBringIntoViewEventArgs> RequestBringIntoViewEvent =
             RoutedEvent.Register<Control, RequestBringIntoViewEventArgs>("RequestBringIntoView", RoutingStrategies.Bubble);
 
-        private Classes _classes = new Classes();
+        private readonly Classes _classes = new Classes();
 
         private DataTemplates _dataTemplates;
 
diff --git a/src/Perspex.Controls/Generators/ItemContainerGenerator.cs b/src/Perspex.Controls/Generators/ItemContainerGenerator.cs
index 39c76ab257..5ec080255e 100644
--- a/src/Perspex.Controls/Generators/ItemContainerGenerator.cs
+++ b/src/Perspex.Controls/Generators/ItemContainerGenerator.cs
@@ -17,7 +17,7 @@ namespace Perspex.Controls.Generators
     {
         private Dictionary<int, IControl> _containers = new Dictionary<int, IControl>();
 
-        private Subject<ItemContainers> _containersInitialized = new Subject<ItemContainers>();
+        private readonly Subject<ItemContainers> _containersInitialized = new Subject<ItemContainers>();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ItemContainerGenerator"/> class.
diff --git a/src/Perspex.Controls/Generators/TreeItemContainerGenerator.cs b/src/Perspex.Controls/Generators/TreeItemContainerGenerator.cs
index 54e87b980d..da6703f0b8 100644
--- a/src/Perspex.Controls/Generators/TreeItemContainerGenerator.cs
+++ b/src/Perspex.Controls/Generators/TreeItemContainerGenerator.cs
@@ -16,9 +16,9 @@ namespace Perspex.Controls.Generators
     /// <typeparam name="T">The type of the container.</typeparam>
     public class TreeItemContainerGenerator<T> : ITreeItemContainerGenerator where T : TreeViewItem, new()
     {
-        private Dictionary<object, T> _containers = new Dictionary<object, T>();
+        private readonly Dictionary<object, T> _containers = new Dictionary<object, T>();
 
-        private Subject<ItemContainers> _containersInitialized = new Subject<ItemContainers>();
+        private readonly Subject<ItemContainers> _containersInitialized = new Subject<ItemContainers>();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="TreeItemContainerGenerator{T}"/> class.
diff --git a/src/Perspex.Controls/Grid.cs b/src/Perspex.Controls/Grid.cs
index e5be0404e5..1cb80e4221 100644
--- a/src/Perspex.Controls/Grid.cs
+++ b/src/Perspex.Controls/Grid.cs
@@ -859,10 +859,10 @@ namespace Perspex.Controls
 
         private struct GridNode
         {
-            public int Row;
-            public int Column;
-            public double Size;
-            public Segment[,] Matrix;
+            public readonly int Row;
+            public readonly int Column;
+            public readonly double Size;
+            public readonly Segment[,] Matrix;
 
             public GridNode(Segment[,] matrix, int row, int col, double size)
             {
diff --git a/src/Perspex.Controls/GridLength.cs b/src/Perspex.Controls/GridLength.cs
index 28e1aa8a46..a18b6b8f4f 100644
--- a/src/Perspex.Controls/GridLength.cs
+++ b/src/Perspex.Controls/GridLength.cs
@@ -33,9 +33,9 @@ namespace Perspex.Controls
     /// </summary>
     public struct GridLength : IEquatable<GridLength>
     {
-        private GridUnitType _type;
+        private readonly GridUnitType _type;
 
-        private double _value;
+        private readonly double _value;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="GridLength"/> struct.
diff --git a/src/Perspex.Controls/MenuItemAccessKeyHandler.cs b/src/Perspex.Controls/MenuItemAccessKeyHandler.cs
index d4d0693efb..7dbf429696 100644
--- a/src/Perspex.Controls/MenuItemAccessKeyHandler.cs
+++ b/src/Perspex.Controls/MenuItemAccessKeyHandler.cs
@@ -17,7 +17,7 @@ namespace Perspex.Controls
         /// <summary>
         /// The registered access keys.
         /// </summary>
-        private List<Tuple<string, IInputElement>> _registered = new List<Tuple<string, IInputElement>>();
+        private readonly List<Tuple<string, IInputElement>> _registered = new List<Tuple<string, IInputElement>>();
 
         /// <summary>
         /// The window to which the handler belongs.
diff --git a/src/Perspex.Controls/Panel.cs b/src/Perspex.Controls/Panel.cs
index d55bb44b06..b3a95ca72c 100644
--- a/src/Perspex.Controls/Panel.cs
+++ b/src/Perspex.Controls/Panel.cs
@@ -18,7 +18,7 @@ namespace Perspex.Controls
     /// </remarks>
     public class Panel : Control, IReparentingControl, IPanel
     {
-        private Controls _children = new Controls();
+        private readonly Controls _children = new Controls();
 
         private ILogical _childLogicalParent;
 
diff --git a/src/Perspex.Controls/Presenters/TextPresenter.cs b/src/Perspex.Controls/Presenters/TextPresenter.cs
index 113a9b952f..d594d6495b 100644
--- a/src/Perspex.Controls/Presenters/TextPresenter.cs
+++ b/src/Perspex.Controls/Presenters/TextPresenter.cs
@@ -21,7 +21,7 @@ namespace Perspex.Controls.Presenters
         public static readonly PerspexProperty<int> SelectionEndProperty =
             TextBox.SelectionEndProperty.AddOwner<TextPresenter>();
 
-        private DispatcherTimer _caretTimer;
+        private readonly DispatcherTimer _caretTimer;
 
         private bool _caretBlink;
 
diff --git a/src/Perspex.Controls/Primitives/AdornerLayer.cs b/src/Perspex.Controls/Primitives/AdornerLayer.cs
index 83d425a960..67ef2e71da 100644
--- a/src/Perspex.Controls/Primitives/AdornerLayer.cs
+++ b/src/Perspex.Controls/Primitives/AdornerLayer.cs
@@ -14,10 +14,10 @@ namespace Perspex.Controls.Primitives
         public static PerspexProperty<Visual> AdornedElementProperty =
             PerspexProperty.RegisterAttached<AdornerLayer, Visual, Visual>("AdornedElement");
 
-        private static PerspexProperty<AdornedElementInfo> s_adornedElementInfoProperty =
+        private static readonly PerspexProperty<AdornedElementInfo> s_adornedElementInfoProperty =
             PerspexProperty.RegisterAttached<AdornerLayer, Visual, AdornedElementInfo>("AdornedElementInfo");
 
-        private BoundsTracker _tracker = new BoundsTracker();
+        private readonly BoundsTracker _tracker = new BoundsTracker();
 
         static AdornerLayer()
         {
diff --git a/src/Perspex.Controls/Primitives/TemplatedControl.cs b/src/Perspex.Controls/Primitives/TemplatedControl.cs
index 0eb037f363..23f5655d6c 100644
--- a/src/Perspex.Controls/Primitives/TemplatedControl.cs
+++ b/src/Perspex.Controls/Primitives/TemplatedControl.cs
@@ -74,7 +74,7 @@ namespace Perspex.Controls.Primitives
 
         private bool _templateApplied;
 
-        private ILogger _templateLog;
+        private readonly ILogger _templateLog;
 
         /// <summary>
         /// Initializes static members of the <see cref="TemplatedControl"/> class.
diff --git a/src/Perspex.Controls/Templates/DataTemplate.cs b/src/Perspex.Controls/Templates/DataTemplate.cs
index 14d50941d4..2c18cfdb13 100644
--- a/src/Perspex.Controls/Templates/DataTemplate.cs
+++ b/src/Perspex.Controls/Templates/DataTemplate.cs
@@ -20,7 +20,7 @@ namespace Perspex.Controls.Templates
         /// <summary>
         /// The implementation of the <see cref="Match"/> method.
         /// </summary>
-        private Func<object, bool> _match;
+        private readonly Func<object, bool> _match;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DataTemplate"/> class.
diff --git a/src/Perspex.Controls/Templates/FuncTemplate`1.cs b/src/Perspex.Controls/Templates/FuncTemplate`1.cs
index 5a01795809..e1321bd664 100644
--- a/src/Perspex.Controls/Templates/FuncTemplate`1.cs
+++ b/src/Perspex.Controls/Templates/FuncTemplate`1.cs
@@ -11,7 +11,7 @@ namespace Perspex.Controls.Templates
     /// <typeparam name="TControl">The type of control.</typeparam>
     public class FuncTemplate<TControl> : ITemplate<TControl> where TControl : IControl
     {
-        private Func<TControl> _func;
+        private readonly Func<TControl> _func;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="FuncTemplate{TControl}"/> class.
diff --git a/src/Perspex.Controls/Templates/FuncTemplate`2.cs b/src/Perspex.Controls/Templates/FuncTemplate`2.cs
index a465e6a01e..d5e997e5d0 100644
--- a/src/Perspex.Controls/Templates/FuncTemplate`2.cs
+++ b/src/Perspex.Controls/Templates/FuncTemplate`2.cs
@@ -13,7 +13,7 @@ namespace Perspex.Controls.Templates
     public class FuncTemplate<TParam, TControl> : ITemplate<TParam, TControl>
         where TControl : IControl
     {
-        private Func<TParam, TControl> _func;
+        private readonly Func<TParam, TControl> _func;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="FuncTemplate{TControl, TParam}"/> class.
diff --git a/src/Perspex.Controls/Templates/TreeDataTemplate.cs b/src/Perspex.Controls/Templates/TreeDataTemplate.cs
index 2d7312b928..e384aaf90d 100644
--- a/src/Perspex.Controls/Templates/TreeDataTemplate.cs
+++ b/src/Perspex.Controls/Templates/TreeDataTemplate.cs
@@ -12,9 +12,9 @@ namespace Perspex.Controls.Templates
     /// </summary>
     public class TreeDataTemplate : DataTemplate, ITreeDataTemplate
     {
-        private Func<object, IEnumerable> _itemsSelector;
+        private readonly Func<object, IEnumerable> _itemsSelector;
 
-        private Func<object, bool> _isExpanded;
+        private readonly Func<object, bool> _isExpanded;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="TreeDataTemplate"/> class.
diff --git a/src/Perspex.Controls/ToolTip.cs b/src/Perspex.Controls/ToolTip.cs
index a65d2c58e3..f2c6e76ffc 100644
--- a/src/Perspex.Controls/ToolTip.cs
+++ b/src/Perspex.Controls/ToolTip.cs
@@ -42,7 +42,7 @@ namespace Perspex.Controls
         /// observable is throttled and calls <see cref="ShowToolTip(Control)"/> when the time
         /// period expires.
         /// </summary>
-        private static Subject<Control> s_show = new Subject<Control>();
+        private static readonly Subject<Control> s_show = new Subject<Control>();
 
         /// <summary>
         /// Initializes static members of the <see cref="ToolTip"/> class.
diff --git a/src/Perspex.Controls/TopLevel.cs b/src/Perspex.Controls/TopLevel.cs
index 15e2c0655b..47e13e41ff 100644
--- a/src/Perspex.Controls/TopLevel.cs
+++ b/src/Perspex.Controls/TopLevel.cs
@@ -47,32 +47,32 @@ namespace Perspex.Controls
         /// <summary>
         /// The dispatcher for the window.
         /// </summary>
-        private Dispatcher _dispatcher;
+        private readonly Dispatcher _dispatcher;
 
         /// <summary>
         /// The render manager for the window.s
         /// </summary>
-        private IRenderManager _renderManager;
+        private readonly IRenderManager _renderManager;
 
         /// <summary>
         /// The window renderer.
         /// </summary>
-        private IRenderer _renderer;
+        private readonly IRenderer _renderer;
 
         /// <summary>
         /// The input manager for the window.
         /// </summary>
-        private IInputManager _inputManager;
+        private readonly IInputManager _inputManager;
 
         /// <summary>
         /// The access key handler for the window.
         /// </summary>
-        private IAccessKeyHandler _accessKeyHandler;
+        private readonly IAccessKeyHandler _accessKeyHandler;
 
         /// <summary>
         /// The access keyboard navigation handler for the window.
         /// </summary>
-        private IKeyboardNavigationHandler _keyboardNavigationHandler;
+        private readonly IKeyboardNavigationHandler _keyboardNavigationHandler;
 
         /// <summary>
         /// Initializes static members of the <see cref="TopLevel"/> class.
diff --git a/src/Perspex.Diagnostics/DevTools.cs b/src/Perspex.Diagnostics/DevTools.cs
index 6431c4f2e8..8bfee0140d 100644
--- a/src/Perspex.Diagnostics/DevTools.cs
+++ b/src/Perspex.Diagnostics/DevTools.cs
@@ -15,7 +15,7 @@ namespace Perspex.Diagnostics
         public static readonly PerspexProperty<Control> RootProperty =
             PerspexProperty.Register<DevTools, Control>("Root");
 
-        private DevToolsViewModel _viewModel;
+        private readonly DevToolsViewModel _viewModel;
 
         public DevTools()
         {
diff --git a/src/Perspex.Diagnostics/ViewModels/DevToolsViewModel.cs b/src/Perspex.Diagnostics/ViewModels/DevToolsViewModel.cs
index a6e0fe91a7..2884e3e604 100644
--- a/src/Perspex.Diagnostics/ViewModels/DevToolsViewModel.cs
+++ b/src/Perspex.Diagnostics/ViewModels/DevToolsViewModel.cs
@@ -17,9 +17,9 @@ namespace Perspex.Diagnostics.ViewModels
 
         private VisualTreeViewModel _visualTree;
 
-        private ObservableAsPropertyHelper<IInputElement> _focusedControl;
+        private readonly ObservableAsPropertyHelper<IInputElement> _focusedControl;
 
-        private ObservableAsPropertyHelper<IInputElement> _pointerOverElement;
+        private readonly ObservableAsPropertyHelper<IInputElement> _pointerOverElement;
 
         public DevToolsViewModel()
         {
diff --git a/src/Perspex.Diagnostics/ViewModels/LogicalTreeViewModel.cs b/src/Perspex.Diagnostics/ViewModels/LogicalTreeViewModel.cs
index 1877beaf76..6d7f31e5ff 100644
--- a/src/Perspex.Diagnostics/ViewModels/LogicalTreeViewModel.cs
+++ b/src/Perspex.Diagnostics/ViewModels/LogicalTreeViewModel.cs
@@ -11,7 +11,7 @@ namespace Perspex.Diagnostics.ViewModels
     {
         private LogicalTreeNode _selected;
 
-        private ObservableAsPropertyHelper<ControlDetailsViewModel> _details;
+        private readonly ObservableAsPropertyHelper<ControlDetailsViewModel> _details;
 
         public LogicalTreeViewModel(Control root)
         {
diff --git a/src/Perspex.Diagnostics/ViewModels/VisualTreeViewModel.cs b/src/Perspex.Diagnostics/ViewModels/VisualTreeViewModel.cs
index c0c951402e..b90be53e87 100644
--- a/src/Perspex.Diagnostics/ViewModels/VisualTreeViewModel.cs
+++ b/src/Perspex.Diagnostics/ViewModels/VisualTreeViewModel.cs
@@ -11,7 +11,7 @@ namespace Perspex.Diagnostics.ViewModels
     {
         private VisualTreeNode _selected;
 
-        private ObservableAsPropertyHelper<ControlDetailsViewModel> _details;
+        private readonly ObservableAsPropertyHelper<ControlDetailsViewModel> _details;
 
         public VisualTreeViewModel(Control root)
         {
diff --git a/src/Perspex.Input/AccessKeyHandler.cs b/src/Perspex.Input/AccessKeyHandler.cs
index 2982a2b536..4cd1a80170 100644
--- a/src/Perspex.Input/AccessKeyHandler.cs
+++ b/src/Perspex.Input/AccessKeyHandler.cs
@@ -26,7 +26,7 @@ namespace Perspex.Input
         /// <summary>
         /// The registered access keys.
         /// </summary>
-        private List<Tuple<string, IInputElement>> _registered = new List<Tuple<string, IInputElement>>();
+        private readonly List<Tuple<string, IInputElement>> _registered = new List<Tuple<string, IInputElement>>();
 
         /// <summary>
         /// The window to which the handler belongs.
diff --git a/src/Perspex.Input/FocusManager.cs b/src/Perspex.Input/FocusManager.cs
index bcfaa4f3a8..74fb29e683 100644
--- a/src/Perspex.Input/FocusManager.cs
+++ b/src/Perspex.Input/FocusManager.cs
@@ -18,7 +18,7 @@ namespace Perspex.Input
         /// <summary>
         /// The focus scopes in which the focus is currently defined.
         /// </summary>
-        private Dictionary<IFocusScope, IInputElement> _focusScopes =
+        private readonly Dictionary<IFocusScope, IInputElement> _focusScopes =
             new Dictionary<IFocusScope, IInputElement>();
 
         /// <summary>
diff --git a/src/Perspex.Input/InputManager.cs b/src/Perspex.Input/InputManager.cs
index 21fbd6e4cb..5b6338b084 100644
--- a/src/Perspex.Input/InputManager.cs
+++ b/src/Perspex.Input/InputManager.cs
@@ -12,9 +12,9 @@ namespace Perspex.Input
 {
     public class InputManager : IInputManager
     {
-        private Subject<RawInputEventArgs> _rawEventReceived = new Subject<RawInputEventArgs>();
+        private readonly Subject<RawInputEventArgs> _rawEventReceived = new Subject<RawInputEventArgs>();
 
-        private Subject<RawInputEventArgs> _postProcess = new Subject<RawInputEventArgs>();
+        private readonly Subject<RawInputEventArgs> _postProcess = new Subject<RawInputEventArgs>();
 
         public static IInputManager Instance => Locator.Current.GetService<IInputManager>();
 
diff --git a/src/Perspex.Input/MouseDevice.cs b/src/Perspex.Input/MouseDevice.cs
index 5c14b70b24..98833b230e 100644
--- a/src/Perspex.Input/MouseDevice.cs
+++ b/src/Perspex.Input/MouseDevice.cs
@@ -21,7 +21,7 @@ namespace Perspex.Input
 
         private uint _lastClickTime;
 
-        private List<IInputElement> _pointerOvers = new List<IInputElement>();
+        private readonly List<IInputElement> _pointerOvers = new List<IInputElement>();
 
         public MouseDevice()
         {
diff --git a/src/Perspex.Interactivity/Interactive.cs b/src/Perspex.Interactivity/Interactive.cs
index b4b772b624..36a2f984ac 100644
--- a/src/Perspex.Interactivity/Interactive.cs
+++ b/src/Perspex.Interactivity/Interactive.cs
@@ -17,7 +17,7 @@ namespace Perspex.Interactivity
     /// </summary>
     public class Interactive : Layoutable, IInteractive
     {
-        private Dictionary<RoutedEvent, List<EventSubscription>> _eventHandlers =
+        private readonly Dictionary<RoutedEvent, List<EventSubscription>> _eventHandlers =
             new Dictionary<RoutedEvent, List<EventSubscription>>();
 
         /// <summary>
diff --git a/src/Perspex.Interactivity/RoutedEvent.cs b/src/Perspex.Interactivity/RoutedEvent.cs
index 200f8008be..0b387821a4 100644
--- a/src/Perspex.Interactivity/RoutedEvent.cs
+++ b/src/Perspex.Interactivity/RoutedEvent.cs
@@ -18,7 +18,7 @@ namespace Perspex.Interactivity
 
     public class RoutedEvent
     {
-        private List<ClassEventSubscription> _subscriptions = new List<ClassEventSubscription>();
+        private readonly List<ClassEventSubscription> _subscriptions = new List<ClassEventSubscription>();
 
         public RoutedEvent(
             string name,
diff --git a/src/Perspex.Layout/LayoutManager.cs b/src/Perspex.Layout/LayoutManager.cs
index 8c96262256..758070a3d1 100644
--- a/src/Perspex.Layout/LayoutManager.cs
+++ b/src/Perspex.Layout/LayoutManager.cs
@@ -31,12 +31,12 @@ namespace Perspex.Layout
         /// <summary>
         /// Called when a layout is needed.
         /// </summary>
-        private Subject<Unit> _layoutNeeded;
+        private readonly Subject<Unit> _layoutNeeded;
 
         /// <summary>
         /// Called when a layout is completed.
         /// </summary>
-        private Subject<Unit> _layoutCompleted;
+        private readonly Subject<Unit> _layoutCompleted;
 
         /// <summary>
         /// Whether a measure is needed on the next layout pass.
@@ -61,7 +61,7 @@ namespace Perspex.Layout
         /// <summary>
         /// The logger to use.
         /// </summary>
-        private ILogger _log;
+        private readonly ILogger _log;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="LayoutManager"/> class.
diff --git a/src/Perspex.Layout/Layoutable.cs b/src/Perspex.Layout/Layoutable.cs
index f372c53603..c46f3b838d 100644
--- a/src/Perspex.Layout/Layoutable.cs
+++ b/src/Perspex.Layout/Layoutable.cs
@@ -130,7 +130,7 @@ namespace Perspex.Layout
 
         private Rect? _previousArrange;
 
-        private ILogger _layoutLog;
+        private readonly ILogger _layoutLog;
 
         /// <summary>
         /// Initializes static members of the <see cref="Layoutable"/> class.
diff --git a/src/Perspex.SceneGraph/Matrix.cs b/src/Perspex.SceneGraph/Matrix.cs
index 8af7e0bd00..baf38fb767 100644
--- a/src/Perspex.SceneGraph/Matrix.cs
+++ b/src/Perspex.SceneGraph/Matrix.cs
@@ -11,12 +11,12 @@ namespace Perspex
     /// </summary>
     public struct Matrix
     {
-        private double _m11;
-        private double _m12;
-        private double _m21;
-        private double _m22;
-        private double _m31;
-        private double _m32;
+        private readonly double _m11;
+        private readonly double _m12;
+        private readonly double _m21;
+        private readonly double _m22;
+        private readonly double _m31;
+        private readonly double _m32;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Matrix"/> struct.
diff --git a/src/Perspex.SceneGraph/Media/PathMarkupParser.cs b/src/Perspex.SceneGraph/Media/PathMarkupParser.cs
index ed0f2be4ea..e02f65caba 100644
--- a/src/Perspex.SceneGraph/Media/PathMarkupParser.cs
+++ b/src/Perspex.SceneGraph/Media/PathMarkupParser.cs
@@ -34,7 +34,7 @@ namespace Perspex.Media
 
         private StreamGeometry _geometry;
 
-        private StreamGeometryContext _context;
+        private readonly StreamGeometryContext _context;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PathMarkupParser"/> class.
diff --git a/src/Perspex.SceneGraph/Media/StreamGeometryContext.cs b/src/Perspex.SceneGraph/Media/StreamGeometryContext.cs
index 7fa2723fe0..1a82149735 100644
--- a/src/Perspex.SceneGraph/Media/StreamGeometryContext.cs
+++ b/src/Perspex.SceneGraph/Media/StreamGeometryContext.cs
@@ -17,7 +17,7 @@ namespace Perspex.Media
     /// TODO: This class is just a wrapper around IStreamGeometryContextImpl: is it needed?
     public class StreamGeometryContext : IDisposable
     {
-        private IStreamGeometryContextImpl _impl;
+        private readonly IStreamGeometryContextImpl _impl;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StreamGeometryContext"/> class.
diff --git a/src/Perspex.SceneGraph/Origin.cs b/src/Perspex.SceneGraph/Origin.cs
index a66014597f..591a2379eb 100644
--- a/src/Perspex.SceneGraph/Origin.cs
+++ b/src/Perspex.SceneGraph/Origin.cs
@@ -31,7 +31,7 @@ namespace Perspex
 
         private Point _point;
 
-        private OriginUnit _unit;
+        private readonly OriginUnit _unit;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Origin"/> struct.
diff --git a/src/Perspex.SceneGraph/Point.cs b/src/Perspex.SceneGraph/Point.cs
index 84a929f6d9..87e97a0d1a 100644
--- a/src/Perspex.SceneGraph/Point.cs
+++ b/src/Perspex.SceneGraph/Point.cs
@@ -13,12 +13,12 @@ namespace Perspex
         /// <summary>
         /// The X position.
         /// </summary>
-        private double _x;
+        private readonly double _x;
 
         /// <summary>
         /// The Y position.
         /// </summary>
-        private double _y;
+        private readonly double _y;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Point"/> structure.
diff --git a/src/Perspex.SceneGraph/Rect.cs b/src/Perspex.SceneGraph/Rect.cs
index e38b84557b..95b08eedd6 100644
--- a/src/Perspex.SceneGraph/Rect.cs
+++ b/src/Perspex.SceneGraph/Rect.cs
@@ -14,22 +14,22 @@ namespace Perspex
         /// <summary>
         /// The X position.
         /// </summary>
-        private double _x;
+        private readonly double _x;
 
         /// <summary>
         /// The Y position.
         /// </summary>
-        private double _y;
+        private readonly double _y;
 
         /// <summary>
         /// The width.
         /// </summary>
-        private double _width;
+        private readonly double _width;
 
         /// <summary>
         /// The height.
         /// </summary>
-        private double _height;
+        private readonly double _height;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Rect"/> structure.
diff --git a/src/Perspex.SceneGraph/Rendering/RenderManager.cs b/src/Perspex.SceneGraph/Rendering/RenderManager.cs
index f2cb619d60..8f89c6d31f 100644
--- a/src/Perspex.SceneGraph/Rendering/RenderManager.cs
+++ b/src/Perspex.SceneGraph/Rendering/RenderManager.cs
@@ -12,7 +12,7 @@ namespace Perspex.Rendering
     /// </summary>
     public class RenderManager : IRenderManager
     {
-        private Subject<Unit> _renderNeeded = new Subject<Unit>();
+        private readonly Subject<Unit> _renderNeeded = new Subject<Unit>();
 
         private bool _renderQueued;
 
diff --git a/src/Perspex.SceneGraph/Size.cs b/src/Perspex.SceneGraph/Size.cs
index 8e15fbbb64..c2aac871e6 100644
--- a/src/Perspex.SceneGraph/Size.cs
+++ b/src/Perspex.SceneGraph/Size.cs
@@ -19,12 +19,12 @@ namespace Perspex
         /// <summary>
         /// The width.
         /// </summary>
-        private double _width;
+        private readonly double _width;
 
         /// <summary>
         /// The height.
         /// </summary>
-        private double _height;
+        private readonly double _height;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Size"/> structure.
diff --git a/src/Perspex.SceneGraph/Thickness.cs b/src/Perspex.SceneGraph/Thickness.cs
index f071645207..9861342e2b 100644
--- a/src/Perspex.SceneGraph/Thickness.cs
+++ b/src/Perspex.SceneGraph/Thickness.cs
@@ -14,22 +14,22 @@ namespace Perspex
         /// <summary>
         /// The thickness on the left.
         /// </summary>
-        private double _left;
+        private readonly double _left;
 
         /// <summary>
         /// The thickness on the top.
         /// </summary>
-        private double _top;
+        private readonly double _top;
 
         /// <summary>
         /// The thickness on the right.
         /// </summary>
-        private double _right;
+        private readonly double _right;
 
         /// <summary>
         /// The thickness on the bottom.
         /// </summary>
-        private double _bottom;
+        private readonly double _bottom;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Thickness"/> structure.
diff --git a/src/Perspex.SceneGraph/Vector.cs b/src/Perspex.SceneGraph/Vector.cs
index 4ae14d17ba..42732e4914 100644
--- a/src/Perspex.SceneGraph/Vector.cs
+++ b/src/Perspex.SceneGraph/Vector.cs
@@ -14,12 +14,12 @@ namespace Perspex
         /// <summary>
         /// The X vector.
         /// </summary>
-        private double _x;
+        private readonly double _x;
 
         /// <summary>
         /// The Y vector.
         /// </summary>
-        private double _y;
+        private readonly double _y;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Vector"/> structure.
diff --git a/src/Perspex.SceneGraph/Visual.cs b/src/Perspex.SceneGraph/Visual.cs
index f37b51cd28..3ede93a78c 100644
--- a/src/Perspex.SceneGraph/Visual.cs
+++ b/src/Perspex.SceneGraph/Visual.cs
@@ -73,7 +73,7 @@ namespace Perspex
         /// <summary>
         /// Holds the children of the visual.
         /// </summary>
-        private PerspexList<IVisual> _visualChildren;
+        private readonly PerspexList<IVisual> _visualChildren;
 
         /// <summary>
         /// Holds the parent of the visual.
@@ -88,7 +88,7 @@ namespace Perspex
         /// <summary>
         /// The logger for visual-level events.
         /// </summary>
-        private ILogger _visualLogger;
+        private readonly ILogger _visualLogger;
 
         /// <summary>
         /// Initializes static members of the <see cref="Visual"/> class.
diff --git a/src/Perspex.Styling/Styling/Classes.cs b/src/Perspex.Styling/Styling/Classes.cs
index d4873e53b7..8cb5be11a6 100644
--- a/src/Perspex.Styling/Styling/Classes.cs
+++ b/src/Perspex.Styling/Styling/Classes.cs
@@ -13,15 +13,15 @@ namespace Perspex.Styling
 {
     public class Classes : ICollection<string>, INotifyCollectionChanged
     {
-        private List<string> _inner;
+        private readonly List<string> _inner;
 
-        private Subject<NotifyCollectionChangedEventArgs> _beforeChanged
+        private readonly Subject<NotifyCollectionChangedEventArgs> _beforeChanged
             = new Subject<NotifyCollectionChangedEventArgs>();
 
-        private Subject<NotifyCollectionChangedEventArgs> _changed
+        private readonly Subject<NotifyCollectionChangedEventArgs> _changed
             = new Subject<NotifyCollectionChangedEventArgs>();
 
-        private Subject<NotifyCollectionChangedEventArgs> _afterChanged
+        private readonly Subject<NotifyCollectionChangedEventArgs> _afterChanged
             = new Subject<NotifyCollectionChangedEventArgs>();
 
         public Classes()
diff --git a/src/Perspex.Styling/Styling/Selector.cs b/src/Perspex.Styling/Styling/Selector.cs
index 30abfc73c6..1f9fb42784 100644
--- a/src/Perspex.Styling/Styling/Selector.cs
+++ b/src/Perspex.Styling/Styling/Selector.cs
@@ -8,11 +8,11 @@ namespace Perspex.Styling
 {
     public class Selector
     {
-        private Func<IStyleable, SelectorMatch> _evaluate;
+        private readonly Func<IStyleable, SelectorMatch> _evaluate;
 
-        private bool _inTemplate;
+        private readonly bool _inTemplate;
 
-        private bool _stopTraversal;
+        private readonly bool _stopTraversal;
 
         private string _description;
 
diff --git a/src/Perspex.Styling/Styling/StyleActivator.cs b/src/Perspex.Styling/Styling/StyleActivator.cs
index 4f47415234..c6b92a4e39 100644
--- a/src/Perspex.Styling/Styling/StyleActivator.cs
+++ b/src/Perspex.Styling/Styling/StyleActivator.cs
@@ -16,13 +16,13 @@ namespace Perspex.Styling
 
     public class StyleActivator : IObservable<bool>, IDisposable
     {
-        private ActivatorMode _mode;
+        private readonly ActivatorMode _mode;
 
-        private bool[] _values;
+        private readonly bool[] _values;
 
-        private List<IDisposable> _subscriptions = new List<IDisposable>();
+        private readonly List<IDisposable> _subscriptions = new List<IDisposable>();
 
-        private List<IObserver<bool>> _observers = new List<IObserver<bool>>();
+        private readonly List<IObserver<bool>> _observers = new List<IObserver<bool>>();
 
         public StyleActivator(
             IList<IObservable<bool>> inputs,
diff --git a/src/Perspex.Styling/Styling/StyleBinding.cs b/src/Perspex.Styling/Styling/StyleBinding.cs
index 3fcfb2c111..61da30a842 100644
--- a/src/Perspex.Styling/Styling/StyleBinding.cs
+++ b/src/Perspex.Styling/Styling/StyleBinding.cs
@@ -22,7 +22,7 @@ namespace Perspex.Styling
         /// <summary>
         /// The activator.
         /// </summary>
-        private IObservable<bool> _activator;
+        private readonly IObservable<bool> _activator;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StyleBinding"/> class.
diff --git a/src/Windows/Perspex.Direct2D1/Direct2D1Platform.cs b/src/Windows/Perspex.Direct2D1/Direct2D1Platform.cs
index 69e5fa99de..0d04bf1994 100644
--- a/src/Windows/Perspex.Direct2D1/Direct2D1Platform.cs
+++ b/src/Windows/Perspex.Direct2D1/Direct2D1Platform.cs
@@ -11,13 +11,13 @@ namespace Perspex.Direct2D1
 {
     public class Direct2D1Platform : IPlatformRenderInterface
     {
-        private static Direct2D1Platform s_instance = new Direct2D1Platform();
+        private static readonly Direct2D1Platform s_instance = new Direct2D1Platform();
 
-        private static SharpDX.Direct2D1.Factory s_d2D1Factory = new SharpDX.Direct2D1.Factory();
+        private static readonly SharpDX.Direct2D1.Factory s_d2D1Factory = new SharpDX.Direct2D1.Factory();
 
-        private static SharpDX.DirectWrite.Factory s_dwfactory = new SharpDX.DirectWrite.Factory();
+        private static readonly SharpDX.DirectWrite.Factory s_dwfactory = new SharpDX.DirectWrite.Factory();
 
-        private static SharpDX.WIC.ImagingFactory s_imagingFactory = new SharpDX.WIC.ImagingFactory();
+        private static readonly SharpDX.WIC.ImagingFactory s_imagingFactory = new SharpDX.WIC.ImagingFactory();
 
         public static void Initialize()
         {
diff --git a/src/Windows/Perspex.Direct2D1/Disposable.cs b/src/Windows/Perspex.Direct2D1/Disposable.cs
index df3573ad88..a7a12ebb9c 100644
--- a/src/Windows/Perspex.Direct2D1/Disposable.cs
+++ b/src/Windows/Perspex.Direct2D1/Disposable.cs
@@ -7,7 +7,7 @@ namespace Perspex.Direct2D1
 {
     public class Disposable<T> : IDisposable where T : IDisposable
     {
-        private IDisposable _extra;
+        private readonly IDisposable _extra;
 
         public Disposable(T inner)
         {
diff --git a/src/Windows/Perspex.Direct2D1/Media/DrawingContext.cs b/src/Windows/Perspex.Direct2D1/Media/DrawingContext.cs
index 975c788a59..8fdcb42b82 100644
--- a/src/Windows/Perspex.Direct2D1/Media/DrawingContext.cs
+++ b/src/Windows/Perspex.Direct2D1/Media/DrawingContext.cs
@@ -18,7 +18,7 @@ namespace Perspex.Direct2D1.Media
         /// <summary>
         /// The Direct2D1 render target.
         /// </summary>
-        private RenderTarget _renderTarget;
+        private readonly RenderTarget _renderTarget;
 
         /// <summary>
         /// The DirectWrite factory.
diff --git a/src/Windows/Perspex.Direct2D1/Media/Imaging/BitmapImpl.cs b/src/Windows/Perspex.Direct2D1/Media/Imaging/BitmapImpl.cs
index a44d59844a..e5347cc5d6 100644
--- a/src/Windows/Perspex.Direct2D1/Media/Imaging/BitmapImpl.cs
+++ b/src/Windows/Perspex.Direct2D1/Media/Imaging/BitmapImpl.cs
@@ -13,7 +13,7 @@ namespace Perspex.Direct2D1.Media
     /// </summary>
     public class BitmapImpl : IBitmapImpl
     {
-        private ImagingFactory _factory;
+        private readonly ImagingFactory _factory;
 
         private SharpDX.Direct2D1.Bitmap _direct2D;
 
diff --git a/src/Windows/Perspex.Direct2D1/Media/Imaging/RenderTargetBitmapImpl.cs b/src/Windows/Perspex.Direct2D1/Media/Imaging/RenderTargetBitmapImpl.cs
index 765fd96163..51f7a71cca 100644
--- a/src/Windows/Perspex.Direct2D1/Media/Imaging/RenderTargetBitmapImpl.cs
+++ b/src/Windows/Perspex.Direct2D1/Media/Imaging/RenderTargetBitmapImpl.cs
@@ -10,7 +10,7 @@ namespace Perspex.Direct2D1.Media
 {
     public class RenderTargetBitmapImpl : BitmapImpl, IRenderTargetBitmapImpl, IDisposable
     {
-        private WicRenderTarget _target;
+        private readonly WicRenderTarget _target;
 
         public RenderTargetBitmapImpl(
             ImagingFactory imagingFactory,
diff --git a/src/Windows/Perspex.Direct2D1/Media/PerspexTextRenderer.cs b/src/Windows/Perspex.Direct2D1/Media/PerspexTextRenderer.cs
index 314f774dd2..dbd56cfa4d 100644
--- a/src/Windows/Perspex.Direct2D1/Media/PerspexTextRenderer.cs
+++ b/src/Windows/Perspex.Direct2D1/Media/PerspexTextRenderer.cs
@@ -10,11 +10,11 @@ namespace Perspex.Direct2D1.Media
 {
     internal class PerspexTextRenderer : TextRenderer
     {
-        private DrawingContext _context;
+        private readonly DrawingContext _context;
 
-        private RenderTarget _renderTarget;
+        private readonly RenderTarget _renderTarget;
 
-        private Brush _foreground;
+        private readonly Brush _foreground;
 
         public PerspexTextRenderer(
             DrawingContext context,
diff --git a/src/Windows/Perspex.Direct2D1/Media/StreamGeometryContextImpl.cs b/src/Windows/Perspex.Direct2D1/Media/StreamGeometryContextImpl.cs
index ae38a75d84..a8021cdb80 100644
--- a/src/Windows/Perspex.Direct2D1/Media/StreamGeometryContextImpl.cs
+++ b/src/Windows/Perspex.Direct2D1/Media/StreamGeometryContextImpl.cs
@@ -8,7 +8,7 @@ namespace Perspex.Direct2D1.Media
 {
     public class StreamGeometryContextImpl : IStreamGeometryContextImpl
     {
-        private GeometrySink _sink;
+        private readonly GeometrySink _sink;
 
         public StreamGeometryContextImpl(GeometrySink sink)
         {
diff --git a/src/Windows/Perspex.Direct2D1/Media/StreamGeometryImpl.cs b/src/Windows/Perspex.Direct2D1/Media/StreamGeometryImpl.cs
index bbafa4a10f..022a53f8c4 100644
--- a/src/Windows/Perspex.Direct2D1/Media/StreamGeometryImpl.cs
+++ b/src/Windows/Perspex.Direct2D1/Media/StreamGeometryImpl.cs
@@ -14,7 +14,7 @@ namespace Perspex.Direct2D1.Media
     /// </summary>
     public class StreamGeometryImpl : GeometryImpl, IStreamGeometryImpl
     {
-        private PathGeometry _path;
+        private readonly PathGeometry _path;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StreamGeometryImpl"/> class.
diff --git a/src/Windows/Perspex.Direct2D1/Renderer.cs b/src/Windows/Perspex.Direct2D1/Renderer.cs
index 92031f31dc..ca628b08a6 100644
--- a/src/Windows/Perspex.Direct2D1/Renderer.cs
+++ b/src/Windows/Perspex.Direct2D1/Renderer.cs
@@ -18,7 +18,7 @@ namespace Perspex.Direct2D1
         /// <summary>
         /// The render target.
         /// </summary>
-        private RenderTarget _renderTarget;
+        private readonly RenderTarget _renderTarget;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Renderer"/> class.
diff --git a/src/Windows/Perspex.Win32/Input/KeyInterop.cs b/src/Windows/Perspex.Win32/Input/KeyInterop.cs
index 3f04af3c4b..658313a27b 100644
--- a/src/Windows/Perspex.Win32/Input/KeyInterop.cs
+++ b/src/Windows/Perspex.Win32/Input/KeyInterop.cs
@@ -10,7 +10,7 @@ namespace Perspex.Win32.Input
 {
     public static class KeyInterop
     {
-        private static Dictionary<Key, int> s_virtualKeyFromKey = new Dictionary<Key, int>
+        private static readonly Dictionary<Key, int> s_virtualKeyFromKey = new Dictionary<Key, int>
         {
             { Key.None, 0 },
             { Key.Cancel, 3 },
@@ -187,7 +187,7 @@ namespace Perspex.Win32.Input
             { Key.DeadCharProcessed, 0 },
         };
 
-        private static Dictionary<int, Key> s_keyFromVirtualKey = new Dictionary<int, Key>
+        private static readonly Dictionary<int, Key> s_keyFromVirtualKey = new Dictionary<int, Key>
         {
             { 0, Key.None },
             { 3, Key.Cancel },
diff --git a/src/Windows/Perspex.Win32/Input/WindowsKeyboardDevice.cs b/src/Windows/Perspex.Win32/Input/WindowsKeyboardDevice.cs
index 46c530092f..0f40007f5b 100644
--- a/src/Windows/Perspex.Win32/Input/WindowsKeyboardDevice.cs
+++ b/src/Windows/Perspex.Win32/Input/WindowsKeyboardDevice.cs
@@ -10,9 +10,9 @@ namespace Perspex.Win32.Input
 {
     public class WindowsKeyboardDevice : KeyboardDevice
     {
-        private static WindowsKeyboardDevice s_instance = new WindowsKeyboardDevice();
+        private static readonly WindowsKeyboardDevice s_instance = new WindowsKeyboardDevice();
 
-        private byte[] _keyStates = new byte[256];
+        private readonly byte[] _keyStates = new byte[256];
 
         public static new WindowsKeyboardDevice Instance => s_instance;
 
diff --git a/src/Windows/Perspex.Win32/Input/WindowsMouseDevice.cs b/src/Windows/Perspex.Win32/Input/WindowsMouseDevice.cs
index 6a26840c62..dd8aafdaa4 100644
--- a/src/Windows/Perspex.Win32/Input/WindowsMouseDevice.cs
+++ b/src/Windows/Perspex.Win32/Input/WindowsMouseDevice.cs
@@ -10,7 +10,7 @@ namespace Perspex.Win32.Input
 {
     public class WindowsMouseDevice : MouseDevice
     {
-        private static WindowsMouseDevice s_instance = new WindowsMouseDevice();
+        private static readonly WindowsMouseDevice s_instance = new WindowsMouseDevice();
 
         public static new WindowsMouseDevice Instance => s_instance;
 
diff --git a/src/Windows/Perspex.Win32/Win32Platform.cs b/src/Windows/Perspex.Win32/Win32Platform.cs
index 1659d33694..da4be6b6a6 100644
--- a/src/Windows/Perspex.Win32/Win32Platform.cs
+++ b/src/Windows/Perspex.Win32/Win32Platform.cs
@@ -18,13 +18,13 @@ namespace Perspex.Win32
 {
     public class Win32Platform : IPlatformThreadingInterface, IPlatformSettings
     {
-        private static Win32Platform s_instance = new Win32Platform();
+        private static readonly Win32Platform s_instance = new Win32Platform();
 
         private UnmanagedMethods.WndProc _wndProcDelegate;
 
         private IntPtr _hwnd;
 
-        private List<Delegate> _delegates = new List<Delegate>();
+        private readonly List<Delegate> _delegates = new List<Delegate>();
 
         public Win32Platform()
         {
diff --git a/src/Windows/Perspex.Win32/WindowImpl.cs b/src/Windows/Perspex.Win32/WindowImpl.cs
index 84982e08ac..75a03b832f 100644
--- a/src/Windows/Perspex.Win32/WindowImpl.cs
+++ b/src/Windows/Perspex.Win32/WindowImpl.cs
@@ -20,7 +20,7 @@ namespace Perspex.Win32
 {
     public class WindowImpl : IWindowImpl
     {
-        private static List<WindowImpl> s_instances = new List<WindowImpl>();
+        private static readonly List<WindowImpl> s_instances = new List<WindowImpl>();
 
         private static readonly IntPtr DefaultCursor = UnmanagedMethods.LoadCursor(
             IntPtr.Zero, new IntPtr((int)UnmanagedMethods.Cursor.IDC_ARROW));
diff --git a/tests/Perspex.RenderTests/Controls/ImageTests.cs b/tests/Perspex.RenderTests/Controls/ImageTests.cs
index 3833bf13be..2f43cbdae1 100644
Binary files a/tests/Perspex.RenderTests/Controls/ImageTests.cs and b/tests/Perspex.RenderTests/Controls/ImageTests.cs differ
diff --git a/tests/Perspex.Styling.UnitTests/TestSubject.cs b/tests/Perspex.Styling.UnitTests/TestSubject.cs
index 37304abd45..042c6e8acd 100644
--- a/tests/Perspex.Styling.UnitTests/TestSubject.cs
+++ b/tests/Perspex.Styling.UnitTests/TestSubject.cs
@@ -9,9 +9,9 @@ namespace Perspex.Styling.UnitTests
 {
     internal class TestSubject<T> : IObserver<T>, IObservable<T>
     {
-        private T _initial;
+        private readonly T _initial;
 
-        private List<IObserver<T>> _subscribers = new List<IObserver<T>>();
+        private readonly List<IObserver<T>> _subscribers = new List<IObserver<T>>();
 
         public TestSubject(T initial)
         {