diff --git a/Perspex.UnitTests/Perspex.UnitTests.csproj b/Perspex.UnitTests/Perspex.UnitTests.csproj
index b07df6a6e8..2996a1fe0b 100644
--- a/Perspex.UnitTests/Perspex.UnitTests.csproj
+++ b/Perspex.UnitTests/Perspex.UnitTests.csproj
@@ -69,6 +69,8 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="PerspexObjectTests.cs" />
     <Compile Include="StyleTests.cs" />
+    <Compile Include="Styling\SelectorTests.cs" />
+    <Compile Include="Styling\SubscribeCheck.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Perspex\Perspex.csproj">
diff --git a/Perspex.UnitTests/StyleTests.cs b/Perspex.UnitTests/StyleTests.cs
index be88fa4f97..f842c2563a 100644
--- a/Perspex.UnitTests/StyleTests.cs
+++ b/Perspex.UnitTests/StyleTests.cs
@@ -18,7 +18,7 @@ namespace Perspex.UnitTests
         [TestMethod]
         public void Style_With_Only_Type_Selector_Should_Update_Value()
         {
-            Style style = new Style(x => x.Select<TextBlock>())
+            Style style = new Style(x => x.Select().OfType<TextBlock>())
             {
                 Setters = new[]
                 {
@@ -38,7 +38,7 @@ namespace Perspex.UnitTests
         [TestMethod]
         public void Style_With_Class_Selector_Should_Update_And_Restore_Value()
         {
-            Style style = new Style(x => x.Select<TextBlock>().Class("foo"))
+            Style style = new Style(x => x.Select().OfType<TextBlock>().Class("foo"))
             {
                 Setters = new[]
                 {
@@ -62,7 +62,7 @@ namespace Perspex.UnitTests
         [TestMethod]
         public void Later_Styles_Should_Override_Earlier()
         {
-            Style style1 = new Style(x => x.Select<TextBlock>().Class("foo"))
+            Style style1 = new Style(x => x.Select().OfType<TextBlock>().Class("foo"))
             {
                 Setters = new[]
                 {
@@ -70,7 +70,7 @@ namespace Perspex.UnitTests
                 },
             };
 
-            Style style2 = new Style(x => x.Select<TextBlock>().Class("foo"))
+            Style style2 = new Style(x => x.Select().OfType<TextBlock>().Class("foo"))
             {
                 Setters = new[]
                 {
diff --git a/Perspex.UnitTests/Styling/SelectorTests.cs b/Perspex.UnitTests/Styling/SelectorTests.cs
new file mode 100644
index 0000000000..45ec6294a1
--- /dev/null
+++ b/Perspex.UnitTests/Styling/SelectorTests.cs
@@ -0,0 +1,68 @@
+// -----------------------------------------------------------------------
+// <copyright file="SelectorTests.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.UnitTests.Styling
+{
+    using System;
+    using System.Linq;
+    using System.Reactive;
+    using System.Reactive.Linq;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+    using Perspex.Styling;
+    using Match = Perspex.Styling.Match;
+
+    [TestClass]
+    public class SelectorTests
+    {
+        [TestMethod]
+        public void OfType_Matches_Control_Of_Correct_Type()
+        {
+            var control = new Class1();
+            var target = control.Select().OfType<Class1>();
+
+            CollectionAssert.AreEqual(new[] { true }, target.GetActivator().Take(1).ToEnumerable().ToArray());
+        }
+
+        [TestMethod]
+        public void OfType_Doesnt_Match_Control_Of_Wrong_Type()
+        {
+            var control = new Class2();
+            var target = control.Select().OfType<Class1>();
+
+            CollectionAssert.AreEqual(new[] { false }, target.GetActivator().Take(1).ToEnumerable().ToArray());
+        }
+
+        [TestMethod]
+        public void When_OfType_Matches_Control_Other_Selectors_Are_Subscribed()
+        {
+            var control = new Class1();
+            var target = control.Select().OfType<Class1>().SubscribeCheck();
+
+            var result = target.GetActivator().ToEnumerable().Take(1).ToArray();
+
+            Assert.AreEqual(1, control.SubscribeCheckObservable.SubscribedCount);
+        }
+
+        [TestMethod]
+        public void When_OfType_Doesnt_Match_Control_Other_Selectors_Are_Not_Subscribed()
+        {
+            var control = new Class1();
+            var target = control.Select().OfType<Class2>().SubscribeCheck();
+
+            var result = target.GetActivator().ToEnumerable().Take(1).ToArray();
+
+            Assert.AreEqual(0, control.SubscribeCheckObservable.SubscribedCount);
+        }
+
+        public class Class1 : SubscribeCheck
+        {
+        }
+
+        public class Class2 : SubscribeCheck
+        {
+        }
+    }
+}
diff --git a/Perspex.UnitTests/Styling/SubscribeCheck.cs b/Perspex.UnitTests/Styling/SubscribeCheck.cs
new file mode 100644
index 0000000000..e6cd0cde76
--- /dev/null
+++ b/Perspex.UnitTests/Styling/SubscribeCheck.cs
@@ -0,0 +1,59 @@
+// -----------------------------------------------------------------------
+// <copyright file="SubscribeCheck.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.UnitTests.Styling
+{
+    using System;
+    using System.Reactive.Disposables;
+    using Perspex.Styling;
+    using Match = Perspex.Styling.Match;
+
+    public class TestObservable : IObservable<bool>
+    {
+        public int SubscribedCount { get; private set; }
+
+        public IDisposable Subscribe(IObserver<bool> observer)
+        {
+            ++this.SubscribedCount;
+            observer.OnNext(true);
+            return Disposable.Create(() => --this.SubscribedCount);
+        }
+    }
+
+    public class SubscribeCheck : IStyleable
+    {
+        public SubscribeCheck()
+        {
+            this.Classes = new PerspexList<string>();
+            this.SubscribeCheckObservable = new TestObservable();
+        }
+
+        public PerspexList<string> Classes
+        {
+            get;
+            private set;
+        }
+
+        public TestObservable SubscribeCheckObservable
+        {
+            get;
+            private set;
+        }
+
+        public virtual void SetValue(PerspexProperty property, object value, IObservable<bool> activator)
+        {
+        }
+    }
+
+    public static class TestSelectors
+    {
+        public static Match SubscribeCheck(this Match match)
+        {
+            match.Observables.Add(((SubscribeCheck)match.Control).SubscribeCheckObservable);
+            return match;
+        }
+    }
+}
diff --git a/Perspex/Perspex.csproj b/Perspex/Perspex.csproj
index ed8045927f..8417ba0679 100644
--- a/Perspex/Perspex.csproj
+++ b/Perspex/Perspex.csproj
@@ -79,6 +79,7 @@
     <Compile Include="ControlTemplate.cs" />
     <Compile Include="Input\MouseEventArgs.cs" />
     <Compile Include="Interactive.cs" />
+    <Compile Include="Styling\Activator.cs" />
     <Compile Include="Styling\IStyleable.cs" />
     <Compile Include="Styling\IStyle.cs" />
     <Compile Include="PriorityValue.cs" />
diff --git a/Perspex/Styling/Activator.cs b/Perspex/Styling/Activator.cs
new file mode 100644
index 0000000000..d8739ae709
--- /dev/null
+++ b/Perspex/Styling/Activator.cs
@@ -0,0 +1,89 @@
+// -----------------------------------------------------------------------
+// <copyright file="Activator.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.Styling
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Diagnostics.Contracts;
+    using System.Linq;
+    using System.Reactive.Disposables;
+
+    public class Activator : IObservable<bool>
+    {
+        List<bool> values = new List<bool>();
+
+        List<IDisposable> subscriptions = new List<IDisposable>();
+
+        List<IObserver<bool>> observers = new List<IObserver<bool>>();
+
+        bool last = false;
+
+        public Activator(IList<IObservable<bool>> observables)
+        {
+            int i = 0;
+
+            foreach (IObservable<bool> o in observables.Reverse())
+            {
+                int iCaptured = i;
+
+                this.values.Add(false);
+
+                IDisposable subscription = o.Subscribe(
+                    x => this.Update(iCaptured, x),
+                    x => this.Finish(iCaptured),
+                    () => this.Finish(iCaptured));
+
+                this.subscriptions.Add(subscription);
+
+                ++i;
+            }
+        }
+
+        public IDisposable Subscribe(IObserver<bool> observer)
+        {
+            Contract.Requires<ArgumentNullException>(observer != null);
+
+            this.observers.Add(observer);
+            observer.OnNext(last);
+            return Disposable.Create(() => this.observers.Remove(observer));
+        }
+
+        private void Update(int index, bool value)
+        {
+            this.values[index] = value;
+
+            bool current = this.values.All(x => x);
+
+            if (current != last)
+            {
+                this.Push(current);
+                last = current;
+            }
+        }
+
+        private void Finish(int i)
+        {
+            if (!this.values[i])
+            {
+                // If the observable has finished on 'false' then it will never go back to true
+                // so we can unsubscribe from all the other subscriptions now.
+                foreach (IDisposable subscription in this.subscriptions)
+                {
+                    subscription.Dispose();
+                }
+            }
+        }
+
+        private void Push(bool value)
+        {
+            foreach (IObserver<bool> observer in this.observers)
+            {
+                observer.OnNext(value);
+            }
+        }
+    }
+}
diff --git a/Perspex/Styling/Match.cs b/Perspex/Styling/Match.cs
index fe74a97576..a05cf66010 100644
--- a/Perspex/Styling/Match.cs
+++ b/Perspex/Styling/Match.cs
@@ -14,54 +14,38 @@ namespace Perspex.Styling
 
     public class Match
     {
-        public IStyleable Control
+        public Match(IStyleable control)
         {
-            get;
-            set;
+            this.Control = control;
+            this.Observables = new List<IObservable<bool>>();
         }
 
-        public IObservable<bool> Observable
+        public IStyleable Control
         {
             get;
-            set;
+            private set;
         }
 
-        public Match Previous
+        public List<IObservable<bool>> Observables
         {
             get;
             set;
         }
 
-        public string Token
+        public string SelectorString
         {
             get;
             set;
         }
 
-        public IObservable<bool> GetActivator()
+        public Activator GetActivator()
         {
-            List<IObservable<bool>> observables = new List<IObservable<bool>>();
-            Match match = this;
-
-            do
-            {
-                if (match.Observable != null)
-                {
-                    observables.Add(match.Observable);
-                }
-
-                match = match.Previous;
-            }
-            while (match != null);
-
-            return System.Reactive.Linq.Observable.CombineLatest(observables).Select(x => x.All(b => b));
+            return new Activator(this.Observables);
         }
 
         public override string ToString()
         {
-            string result = (this.Previous != null) ? this.Previous.ToString() : string.Empty;
-            result += this.Token;
-            return result;
+            return this.SelectorString;
         }
     }
 }
diff --git a/Perspex/Styling/Selectors.cs b/Perspex/Styling/Selectors.cs
index bc8e071a22..f7994dde95 100644
--- a/Perspex/Styling/Selectors.cs
+++ b/Perspex/Styling/Selectors.cs
@@ -18,47 +18,33 @@ namespace Perspex.Styling
 
     public static class Selectors
     {
-        public static Match Select<T>(this IStyleable control)
+        public static Match Select(this IStyleable control)
         {
             Contract.Requires<ArgumentNullException>(control != null);
 
-            if (control is T)
-            {
-                return new Match
-                {
-                    Control = control,
-                    Observable = Observable.Return(true),
-                    Token = typeof(T).Name,
-                };
-            }
-            else
-            {
-                return null;
-            }
+            return new Match(control);
         }
 
-        public static Match Class(this Match selector, string name)
+        public static Match Class(this Match match, string name)
         {
+            Contract.Requires<ArgumentNullException>(match != null);
             Contract.Requires<ArgumentNullException>(name != null);
 
-            if (selector != null)
-            {
-                IObservable<bool> match = Observable
-                    .Return(selector.Control.Classes.Contains(name))
-                    .Concat(selector.Control.Classes.Changed.Select(e => selector.Control.Classes.Contains(name)));
+            match.Observables.Add(Observable
+                .Return(match.Control.Classes.Contains(name))
+                .Concat(match.Control.Classes.Changed.Select(e => match.Control.Classes.Contains(name))));
+            match.SelectorString += (name[0] == ':') ? name : '.' + name;
 
-                return new Match
-                {
-                    Control = selector.Control,
-                    Observable = match,
-                    Previous = selector,
-                    Token = (name[0] == ':') ? name : '.' + name,
-                };
-            }
-            else
-            {
-                return null;
-            }
+            return match;
+        }
+
+        public static Match OfType<T>(this Match match)
+        {
+            Contract.Requires<ArgumentNullException>(match != null);
+
+            match.Observables.Add(Observable.Return(match.Control is T));
+            match.SelectorString += typeof(T).Name;
+            return match;
         }
     }
 }
diff --git a/Perspex/Themes/Default/ButtonStyle.cs b/Perspex/Themes/Default/ButtonStyle.cs
index f04990d3e8..923dfd010a 100644
--- a/Perspex/Themes/Default/ButtonStyle.cs
+++ b/Perspex/Themes/Default/ButtonStyle.cs
@@ -15,7 +15,7 @@ namespace Perspex.Themes.Default
         {
             this.AddRange(new[]
             {
-                new Style(x => x.Select<Button>())
+                new Style(x => x.Select().OfType<Button>())
                 {
                     Setters = new[]
                     {
@@ -26,7 +26,7 @@ namespace Perspex.Themes.Default
                         new Setter(Button.TemplateProperty, ControlTemplate.Create<Button>(this.Template)),
                     },
                 },
-                new Style(x => x.Select<Button>().Class(":mouseover"))
+                new Style(x => x.Select().OfType<Button>().Class(":mouseover"))
                 {
                     Setters = new[]
                     {
@@ -34,7 +34,7 @@ namespace Perspex.Themes.Default
                         new Setter (Button.BorderBrushProperty, new SolidColorBrush(0xff3c7fb1)),
                     },
                 },
-                new Style(x => x.Select<Button>().Class(":pressed"))
+                new Style(x => x.Select().OfType<Button>().Class(":pressed"))
                 {
                     Setters = new[]
                     {