diff --git a/Perspex.UnitTests/Perspex.UnitTests.csproj b/Perspex.UnitTests/Perspex.UnitTests.csproj
index a9d5b5368c..5f26677796 100644
--- a/Perspex.UnitTests/Perspex.UnitTests.csproj
+++ b/Perspex.UnitTests/Perspex.UnitTests.csproj
@@ -72,11 +72,14 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="PerspexObjectTests.cs" />
     <Compile Include="StyleTests.cs" />
+    <Compile Include="Styling\ActivatorTests.cs" />
     <Compile Include="Styling\SelectorTests_Class.cs" />
     <Compile Include="Styling\SelectorTests_Id.cs" />
     <Compile Include="Styling\SelectorTests_OfType.cs" />
     <Compile Include="Styling\SelectorTests_Template.cs" />
     <Compile Include="Styling\TestControlBase.cs" />
+    <Compile Include="TestSubject.cs" />
+    <Compile Include="TestObserver.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Perspex\Perspex.csproj">
diff --git a/Perspex.UnitTests/Styling/ActivatorTests.cs b/Perspex.UnitTests/Styling/ActivatorTests.cs
new file mode 100644
index 0000000000..3e27529bf3
--- /dev/null
+++ b/Perspex.UnitTests/Styling/ActivatorTests.cs
@@ -0,0 +1,109 @@
+namespace Perspex.UnitTests.Styling
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Reactive.Linq;
+    using System.Reactive.Subjects;
+    using System.Text;
+    using System.Threading.Tasks;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+    using Perspex.Styling;
+    using Activator = Perspex.Styling.Activator;
+
+    [TestClass]
+    public class ActivatorTests
+    {
+        [TestMethod]
+        public void Activator_Should_Follow_Single_Input()
+        {
+            var inputs = new[] { new TestSubject<bool>(false) };
+            var target = new Activator(inputs);
+            var result = new TestObserver<bool>();
+
+            target.Subscribe(result);
+            Assert.IsFalse(result.GetValue());
+            inputs[0].OnNext(true);
+            Assert.IsTrue(result.GetValue());
+            inputs[0].OnNext(false);
+            Assert.IsFalse(result.GetValue());
+            inputs[0].OnNext(true);
+            Assert.IsTrue(result.GetValue());
+
+            Assert.AreEqual(1, inputs[0].SubscriberCount);
+        }
+
+        [TestMethod]
+        public void Activator_Should_AND_Multiple_Inputs()
+        {
+            var inputs = new[] 
+            { 
+                new TestSubject<bool>(false),
+                new TestSubject<bool>(false),
+                new TestSubject<bool>(true),
+            };
+            var target = new Activator(inputs);
+            var result = new TestObserver<bool>();
+
+            target.Subscribe(result);
+            Assert.IsFalse(result.GetValue());
+            inputs[0].OnNext(true);
+            inputs[1].OnNext(true);
+            Assert.IsTrue(result.GetValue());
+            inputs[0].OnNext(false);
+            Assert.IsFalse(result.GetValue());
+
+            Assert.AreEqual(1, inputs[0].SubscriberCount);
+            Assert.AreEqual(1, inputs[1].SubscriberCount);
+            Assert.AreEqual(1, inputs[2].SubscriberCount);
+        }
+
+        [TestMethod]
+        public void Activator_Should_Unsubscribe_All_When_Input_Completes_On_False()
+        {
+            var inputs = new[] 
+            { 
+                new TestSubject<bool>(false),
+                new TestSubject<bool>(false),
+                new TestSubject<bool>(true),
+            };
+            var target = new Activator(inputs);
+            var result = new TestObserver<bool>();
+
+            target.Subscribe(result);
+            Assert.IsFalse(result.GetValue());
+            inputs[0].OnNext(true);
+            inputs[1].OnNext(true);
+            Assert.IsTrue(result.GetValue());
+            inputs[0].OnNext(false);
+            Assert.IsFalse(result.GetValue());
+            inputs[0].OnCompleted();
+
+            Assert.AreEqual(0, inputs[0].SubscriberCount);
+            Assert.AreEqual(0, inputs[1].SubscriberCount);
+            Assert.AreEqual(0, inputs[2].SubscriberCount);
+        }
+
+        [TestMethod]
+        public void Activator_Should_Not_Unsubscribe_All_When_Input_Completes_On_False()
+        {
+            var inputs = new[] 
+            { 
+                new TestSubject<bool>(false),
+                new TestSubject<bool>(false),
+                new TestSubject<bool>(true),
+            };
+            var target = new Activator(inputs);
+            var result = new TestObserver<bool>();
+
+            target.Subscribe(result);
+            Assert.IsFalse(result.GetValue());
+            inputs[0].OnNext(true);
+            inputs[0].OnCompleted();
+
+            Assert.AreEqual(1, inputs[0].SubscriberCount);
+            Assert.AreEqual(1, inputs[1].SubscriberCount);
+            Assert.AreEqual(1, inputs[2].SubscriberCount);
+        }
+    }
+}
diff --git a/Perspex.UnitTests/TestObserver.cs b/Perspex.UnitTests/TestObserver.cs
new file mode 100644
index 0000000000..aeee1d4cac
--- /dev/null
+++ b/Perspex.UnitTests/TestObserver.cs
@@ -0,0 +1,65 @@
+// -----------------------------------------------------------------------
+// <copyright file="TestObserver.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.UnitTests
+{
+    using System;
+
+    internal class TestObserver<T> : IObserver<T>
+    {
+        private bool hasValue;
+
+        private T value;
+
+        public bool Completed { get; private set; }
+
+        public Exception Error { get; private set; }
+
+        public T GetValue()
+        {
+            if (!this.hasValue)
+            {
+                throw new Exception("Observable provided no value.");
+            }
+
+            if (this.Completed)
+            {
+                throw new Exception("Observable completed unexpectedly.");
+            }
+
+            if (this.Error != null)
+            {
+                throw new Exception("Observable errored unexpectedly.");
+            }
+
+            this.hasValue = false;
+            return value;
+        }
+
+        public void OnCompleted()
+        {
+            this.Completed = true;
+        }
+
+        public void OnError(Exception error)
+        {
+            this.Error = error;
+        }
+
+        public void OnNext(T value)
+        {
+            if (!this.hasValue)
+            {
+                this.value = value;
+                this.hasValue = true;
+            }
+            else
+            {
+                throw new Exception("Observable pushed more than one value.");
+            }
+        }
+    }
+}
diff --git a/Perspex.UnitTests/TestSubject.cs b/Perspex.UnitTests/TestSubject.cs
new file mode 100644
index 0000000000..0a99a5df93
--- /dev/null
+++ b/Perspex.UnitTests/TestSubject.cs
@@ -0,0 +1,60 @@
+// -----------------------------------------------------------------------
+// <copyright file="TestSubject.cs" company="Steven Kirk">
+// Copyright 2014 MIT Licence. See licence.md for more information.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Perspex.UnitTests
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Reactive.Disposables;
+
+    internal class TestSubject<T> : IObserver<T>, IObservable<T>
+    {
+        private T initial;
+
+        private List<IObserver<T>> subscribers = new List<IObserver<T>>();
+
+        public TestSubject(T initial)
+        {
+            this.initial = initial;
+        }
+
+        public int SubscriberCount
+        {
+            get { return this.subscribers.Count; }
+        }
+
+        public void OnCompleted()
+        {
+            foreach (IObserver<T> subscriber in this.subscribers.ToArray())
+            {
+                subscriber.OnCompleted();
+            }
+        }
+
+        public void OnError(Exception error)
+        {
+            foreach (IObserver<T> subscriber in this.subscribers.ToArray())
+            {
+                subscriber.OnError(error);
+            }
+        }
+
+        public void OnNext(T value)
+        {
+            foreach (IObserver<T> subscriber in this.subscribers.ToArray())
+            {
+                subscriber.OnNext(value);
+            }
+        }
+
+        public IDisposable Subscribe(IObserver<T> observer)
+        {
+            this.subscribers.Add(observer);
+            observer.OnNext(initial);
+            return Disposable.Create(() => this.subscribers.Remove(observer));
+        }
+    }
+}