diff --git a/Nuclex.Support (PC).csproj b/Nuclex.Support (PC).csproj
index 6823b43..4a20885 100644
--- a/Nuclex.Support (PC).csproj	
+++ b/Nuclex.Support (PC).csproj	
@@ -164,6 +164,11 @@
       <XNAUseContentPipeline>false</XNAUseContentPipeline>
       <Name>ThreadedMethodOperation</Name>
     </Compile>
+    <Compile Include="Source\Tracking\SetProgression.Test.cs">
+      <XNAUseContentPipeline>false</XNAUseContentPipeline>
+      <Name>SetProgression.Test</Name>
+      <DependentUpon>SetProgression.cs</DependentUpon>
+    </Compile>
     <Compile Include="Source\Tracking\WeightedProgression.cs">
       <XNAUseContentPipeline>false</XNAUseContentPipeline>
       <Name>WeightedProgression</Name>
diff --git a/Source/Collections/ObservableCollection.Test.cs b/Source/Collections/ObservableCollection.Test.cs
index 7cb1afd..2137d36 100644
--- a/Source/Collections/ObservableCollection.Test.cs
+++ b/Source/Collections/ObservableCollection.Test.cs
@@ -49,35 +49,36 @@ namespace Nuclex.Support.Collections {
         new EventHandler<ObservableCollection<int>.ItemEventArgs>(
           this.mockedSubscriber.ItemRemoved
         );
+
+      this.mockery.VerifyAllExpectationsHaveBeenMet();
     }
 
     /// <summary>Tests whether the Clearing event is fired</summary>
     [Test]
     public void TestClearingEvent() {
-
       Expect.Once.On(this.mockedSubscriber).
         Method("Clearing");
 
       this.observedCollection.Clear();
 
+      this.mockery.VerifyAllExpectationsHaveBeenMet();
     }
 
     /// <summary>Tests whether the ItemAdded event is fired</summary>
     [Test]
     public void TestItemAddedEvent() {
-
       Expect.Once.On(this.mockedSubscriber).
         Method("ItemAdded").
         WithAnyArguments();
 
       this.observedCollection.Add(123);
 
+      this.mockery.VerifyAllExpectationsHaveBeenMet();
     }
 
     /// <summary>Tests whether the ItemRemoved event is fired</summary>
     [Test]
     public void TestItemRemovedEvent() {
-
       Expect.Once.On(this.mockedSubscriber).
         Method("ItemAdded").
         WithAnyArguments();
@@ -89,6 +90,7 @@ namespace Nuclex.Support.Collections {
       this.observedCollection.Add(123);
       this.observedCollection.Remove(123);
 
+      this.mockery.VerifyAllExpectationsHaveBeenMet();
     }
 
     /// <summary>Mock object factory</summary>
diff --git a/Source/Tracking/Internal/ObservedProgression.cs b/Source/Tracking/Internal/ObservedProgression.cs
index 0da1b75..aab0d8d 100644
--- a/Source/Tracking/Internal/ObservedProgression.cs
+++ b/Source/Tracking/Internal/ObservedProgression.cs
@@ -8,34 +8,105 @@ namespace Nuclex.Support.Tracking {
   /// <typeparam name="ProgressionType">
   ///   Type of the progression that is being observed
   /// </typeparam>
-  internal class ObservedProgression<ProgressionType>
+  internal class ObservedProgression<ProgressionType> : IDisposable
     where ProgressionType : Progression {
 
+    /// <summary>Delegate for reporting progress updates</summary>
+    public delegate void ReportDelegate();
+
     /// <summary>Initializes a new observed progression</summary>
     /// <param name="weightedProgression">Weighted progression being observed</param>
+    /// <param name="progressUpdateCallback">
+    ///   Callback to invoke when the progression's progress changes
+    /// </param>
+    /// <param name="endedCallback">
+    ///   Callback to invoke when the progression has ended
+    /// </param>
     internal ObservedProgression(
-      WeightedProgression<ProgressionType> weightedProgression
+      WeightedProgression<ProgressionType> weightedProgression,
+      ReportDelegate progressUpdateCallback,
+      ReportDelegate endedCallback
     ) {
       this.weightedProgression = weightedProgression;
+      this.endedCallback = endedCallback;
+      this.progressUpdateCallback = progressUpdateCallback;
+
+      this.weightedProgression.Progression.AsyncEnded +=
+        new EventHandler(asyncEnded);
+
+      this.weightedProgression.Progression.AsyncProgressUpdated +=
+        new EventHandler<ProgressUpdateEventArgs>(asyncProgressUpdated);
     }
-    
+
+    /// <summary>Immediately releases all resources owned by the object</summary>
+    public void Dispose() {
+      disconnectEvents();
+    }
+
     /// <summary>Weighted progression being observed</summary>
     public WeightedProgression<ProgressionType> WeightedProgression {
       get { return this.weightedProgression; }
     }
-/*
 
-    internal void AsyncProgressUpdated(object sender, ProgressUpdateEventArgs e) {
-      this.Progress = e.Progress;
+    /// <summary>Amount of progress this progression has achieved so far</summary>
+    public float Progress {
+      get { return this.progress; }
     }
-    internal void AsyncEnded(object sender, EventArgs e) { }
-*/
+
+    /// <summary>Called when the observed progression has ended</summary>
+    /// <param name="sender">Progression that has ended</param>
+    /// <param name="e">Not used</param>
+    private void asyncEnded(object sender, EventArgs e) {
+      this.progress = 1.0f;
+
+      disconnectEvents(); // We don't need those anymore!
+
+      this.progressUpdateCallback();
+    }
+
+    /// <summary>Called when the progress of the observed progression changes</summary>
+    /// <param name="sender">Progression whose progress has changed</param>
+    /// <param name="e">Contains the updated progress</param>
+    private void asyncProgressUpdated(object sender, ProgressUpdateEventArgs e) {
+      this.progress = e.Progress;
+
+      this.progressUpdateCallback();
+    }
+
+    /// <summary>Unscribes from all events of the observed progression</summary>
+    private void disconnectEvents() {
+
+      // Make use of the double check locking idiom to avoid the costly lock when
+      // the events have already been unsubscribed
+      if(this.endedCallback != null) {
+
+        // This is an internal class with special knowledge that there
+        // is no risk of deadlock involved, so we don't need a fancy syncRoot!
+        lock(this) {
+          if(this.endedCallback != null) {
+            this.weightedProgression.Progression.AsyncEnded -=
+              new EventHandler(asyncEnded);
+
+            this.weightedProgression.Progression.AsyncProgressUpdated -=
+              new EventHandler<ProgressUpdateEventArgs>(asyncProgressUpdated);
+
+            this.endedCallback = null;
+            this.progressUpdateCallback = null;
+          }
+        }
+
+      } // endedCallback != null
+
+    }
+
     /// <summary>The weighted progression that is being observed</summary>
     private WeightedProgression<ProgressionType> weightedProgression;
-/*
-    /// <summary>Amount of progress this progression has achieved so far</summary>
+    /// <summary>Callback to invoke when the progress updates</summary>
+    private volatile ReportDelegate progressUpdateCallback;
+    /// <summary>Callback to invoke when the progression ends</summary>
+    private volatile ReportDelegate endedCallback;
+    /// <summary>Progress achieved so far</summary>
     private volatile float progress;
-*/
   }
 
 } // namespace Nuclex.Support.Tracking
diff --git a/Source/Tracking/Internal/WeightedProgressionWrapperCollection.cs b/Source/Tracking/Internal/WeightedProgressionWrapperCollection.cs
index 97e6598..550cad9 100644
--- a/Source/Tracking/Internal/WeightedProgressionWrapperCollection.cs
+++ b/Source/Tracking/Internal/WeightedProgressionWrapperCollection.cs
@@ -27,7 +27,7 @@ namespace Nuclex.Support.Tracking {
   ///     SetProgression or QueueOperation classes was created.
   ///   </para>
   /// </remarks>
-  internal class WeightedProgressionCollection<ProgressionType> :
+  internal class WeightedProgressionWrapperCollection<ProgressionType> :
     TransformingReadOnlyCollection<
       ObservedProgression<ProgressionType>, WeightedProgression<ProgressionType>
     >
@@ -35,7 +35,7 @@ namespace Nuclex.Support.Tracking {
 
     /// <summary>Initializes a new weighted progression collection wrapper</summary>
     /// <param name="items">Items to be exposed as weighted progressions</param>
-    internal WeightedProgressionCollection(
+    internal WeightedProgressionWrapperCollection(
       IList<ObservedProgression<ProgressionType>> items
     )
       : base(items) { }
diff --git a/Source/Tracking/ProgressUpdateEventArgs.cs b/Source/Tracking/ProgressUpdateEventArgs.cs
index 7e50889..c44a8d0 100644
--- a/Source/Tracking/ProgressUpdateEventArgs.cs
+++ b/Source/Tracking/ProgressUpdateEventArgs.cs
@@ -19,7 +19,7 @@ namespace Nuclex.Support.Tracking {
     }
 
     /// <summary>Achieved progress</summary>
-    protected float progress;
+    private float progress;
 
   }
 
diff --git a/Source/Tracking/Progression.cs b/Source/Tracking/Progression.cs
index 66c0447..05a20cd 100644
--- a/Source/Tracking/Progression.cs
+++ b/Source/Tracking/Progression.cs
@@ -52,17 +52,21 @@ namespace Nuclex.Support.Tracking {
     public event EventHandler AsyncEnded;
 
     /// <summary>Whether the progression has ended already</summary>
-    public virtual bool Ended {
+    public bool Ended {
       get { return this.ended; }
     }
 
     /// <summary>WaitHandle that can be used to wait for the progression to end</summary>
     public WaitHandle WaitHandle {
       get {
-        
+
         // The WaitHandle will only be created when someone asks for it!
         // See the Double-Check Locking idiom on why the condition is checked twice
         // (primarily, it avoids an expensive lock when it isn't needed)
+        //
+        // We can *not* optimize this lock away since we absolutely must not create
+        // two doneEvents -- someone might call .WaitOne() on the first one when only
+        // the second one is assigned to this.doneEvent and gets set in the end.
         if(this.doneEvent == null) {
 
           lock(this.syncRoot) {
@@ -109,16 +113,27 @@ namespace Nuclex.Support.Tracking {
     ///   seperately.
     /// </remarks>
     protected virtual void OnAsyncEnded() {
+
+      // TODO: Find a way around this. Interlocked.Exchange would be best!
+      // We do not lock here since we require this method to be called only once
+      // in the object's lifetime. If someone really badly wanted to break this
+      // he'd probably have a one-in-a-million chance of getting through.
+      if(this.ended)
+        throw new InvalidOperationException("The progression has already been ended");
+
       this.ended = true;
 
-      lock(this.syncRoot) {
-        if(this.doneEvent != null)
-          this.doneEvent.Set();
-      }
+      // Doesn't need a lock. If another thread wins the race and creates the event
+      // after we just saw it being null, it would be created in an already set
+      // state due to the ended flag (see above) being set to true beforehand!
+      if(this.doneEvent != null)
+        this.doneEvent.Set();
 
+      // Finally, fire the AsyncEnded event
       EventHandler copy = AsyncEnded;
       if(copy != null)
         copy(this, EventArgs.Empty);
+
     }
 
     /// <summary>Used to synchronize multithreaded accesses to this object</summary>
diff --git a/Source/Tracking/SetProgression.Test.cs b/Source/Tracking/SetProgression.Test.cs
new file mode 100644
index 0000000..f39658f
--- /dev/null
+++ b/Source/Tracking/SetProgression.Test.cs
@@ -0,0 +1,215 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+#if UNITTEST
+
+using NUnit.Framework;
+using NMock2;
+
+namespace Nuclex.Support.Tracking {
+
+  /// <summary>Unit Test for the progression set class</summary>
+  [TestFixture]
+  public class SetProgressionTest {
+
+    #region interface ISetProgressionSubscriber
+
+    /// <summary>Interface used to test the set progression.</summary>
+    public interface ISetProgressionSubscriber {
+
+      /// <summary>Called when the set progression's progress changes</summary>
+      /// <param name="sender">Set progression whose progress has changed</param>
+      /// <param name="e">Contains the new progress achieved</param>
+      void ProgressUpdated(object sender, ProgressUpdateEventArgs e);
+
+      /// <summary>Called when the set progression has ended</summary>
+      /// <param name="sender">Set progression that as ended</param>
+      /// <param name="e">Not used</param>
+      void Ended(object sender, EventArgs e);
+
+    }
+
+    #endregion // interface ISetProgressionSubscriber
+
+    #region class ProgressUpdateEventArgsMatcher
+
+    /// <summary>Compares two ProgressUpdateEventArgsInstances for NMock validation</summary>
+    private class ProgressUpdateEventArgsMatcher : Matcher {
+
+      /// <summary>Initializes a new ProgressUpdateEventArgsMatcher </summary>
+      /// <param name="expected">Expected progress update event arguments</param>
+      public ProgressUpdateEventArgsMatcher(ProgressUpdateEventArgs expected) {
+        this.expected = expected;
+      }
+
+      /// <summary>
+      ///   Called by NMock to verfiy the ProgressUpdateEventArgs match the expected value
+      /// </summary>
+      /// <param name="actualAsObject">Actual value to compare to the expected value</param>
+      /// <returns>
+      ///   True if the actual value matches the expected value; otherwise false
+      /// </returns>
+      public override bool Matches(object actualAsObject) {
+        ProgressUpdateEventArgs actual = (actualAsObject as ProgressUpdateEventArgs);
+        if(actual == null)
+          return false;
+
+        return (actual.Progress == this.expected.Progress);
+      }
+
+      /// <summary>Creates a string representation of the expected value</summary>
+      /// <param name="writer">Writer to write the string representation into</param>
+      public override void DescribeTo(TextWriter writer) {
+        writer.Write(this.expected.Progress.ToString());
+      }
+
+      /// <summary>Expected progress update event args value</summary>
+      private ProgressUpdateEventArgs expected;
+
+    }
+
+    #endregion // class ProgressUpdateEventArgsMatcher
+
+    #region class TestProgression
+
+    /// <summary>Progression used for testing in this unit test</summary>
+    private class TestProgression : Progression {
+
+      /// <summary>Changes the testing progression's indicated progress</summary>
+      /// <param name="progress">
+      ///   New progress to be reported by the testing progression
+      /// </param>
+      public void ChangeProgress(float progress) {
+        OnAsyncProgressUpdated(progress);
+      }
+
+      /// <summary>Transitions the progression into the ended state</summary>
+      public void End() {
+        OnAsyncEnded();
+      }
+
+    }
+
+    #endregion // class TestProgression
+
+    /// <summary>Initialization routine executed before each test is run</summary>
+    [SetUp]
+    public void Setup() {
+      this.mockery = new Mockery();
+    }
+
+    /// <summary>Validates that the set progression properly sums the progress</summary>
+    [Test]
+    public void TestSummedProgress() {
+      SetProgression<TestProgression> testSetProgression =
+        new SetProgression<TestProgression>(
+          new TestProgression[] {
+            new TestProgression(), new TestProgression()
+          }
+        );
+
+      ISetProgressionSubscriber mockedSubscriber = mockSubscriber(testSetProgression);
+
+      Expect.Once.On(mockedSubscriber).
+        Method("ProgressUpdated").
+        With(
+          new Matcher[] {
+            new NMock2.Matchers.TypeMatcher(typeof(SetProgression<TestProgression>)),
+            new ProgressUpdateEventArgsMatcher(new ProgressUpdateEventArgs(0.25f))
+          }
+        );
+
+      testSetProgression.Childs[0].Progression.ChangeProgress(0.5f);
+
+      this.mockery.VerifyAllExpectationsHaveBeenMet();
+    }
+
+    /// <summary>Validates that the set progression respects the weights</summary>
+    [Test]
+    public void TestWeightedSummedProgress() {
+      SetProgression<TestProgression> testSetProgression =
+        new SetProgression<TestProgression>(
+          new WeightedProgression<TestProgression>[] {
+            new WeightedProgression<TestProgression>(new TestProgression(), 1.0f),
+            new WeightedProgression<TestProgression>(new TestProgression(), 2.0f)
+          }
+        );
+
+      ISetProgressionSubscriber mockedSubscriber = mockSubscriber(testSetProgression);
+
+      Expect.Once.On(mockedSubscriber).
+        Method("ProgressUpdated").
+        With(
+          new Matcher[] {
+            new NMock2.Matchers.TypeMatcher(typeof(SetProgression<TestProgression>)),
+            new ProgressUpdateEventArgsMatcher(new ProgressUpdateEventArgs(0.5f / 3.0f))
+          }
+        );
+
+      testSetProgression.Childs[0].Progression.ChangeProgress(0.5f);
+
+      Expect.Once.On(mockedSubscriber).
+        Method("ProgressUpdated").
+        With(
+          new Matcher[] {
+            new NMock2.Matchers.TypeMatcher(typeof(SetProgression<TestProgression>)),
+            new ProgressUpdateEventArgsMatcher(new ProgressUpdateEventArgs(0.5f))
+          }
+        );
+
+      testSetProgression.Childs[1].Progression.ChangeProgress(0.5f);
+
+      this.mockery.VerifyAllExpectationsHaveBeenMet();
+    }
+
+    /// <summary>Mocks a subscriber for the events of a progression</summary>
+    /// <param name="progression">Progression to mock an event subscriber for</param>
+    /// <returns>The mocked event subscriber</returns>
+    private ISetProgressionSubscriber mockSubscriber(Progression progression) {
+      ISetProgressionSubscriber mockedSubscriber =
+        this.mockery.NewMock<ISetProgressionSubscriber>();
+
+      progression.AsyncEnded += new EventHandler(mockedSubscriber.Ended);
+      progression.AsyncProgressUpdated +=
+        new EventHandler<ProgressUpdateEventArgs>(mockedSubscriber.ProgressUpdated);
+
+      return mockedSubscriber;
+    }
+
+    /// <summary>
+    ///   Validates that the ended event is triggered when the last progression ends
+    /// </summary>
+    [Test]
+    public void TestEndedEvent() {
+      SetProgression<TestProgression> testSetProgression =
+        new SetProgression<TestProgression>(
+          new TestProgression[] {
+            new TestProgression(), new TestProgression()
+          }
+        );
+
+      ISetProgressionSubscriber mockedSubscriber = mockSubscriber(testSetProgression);
+
+      Expect.Exactly(2).On(mockedSubscriber).
+        Method("ProgressUpdated").
+        WithAnyArguments();
+
+      Expect.Once.On(mockedSubscriber).
+        Method("Ended").
+        WithAnyArguments();
+      
+      testSetProgression.Childs[0].Progression.End();
+      testSetProgression.Childs[1].Progression.End();
+
+      this.mockery.VerifyAllExpectationsHaveBeenMet();
+    }
+
+    /// <summary>Mock object factory</summary>
+    private Mockery mockery;
+
+  }
+
+} // namespace Nuclex.Support.Tracking
+
+#endif // UNITTEST
diff --git a/Source/Tracking/SetProgression.cs b/Source/Tracking/SetProgression.cs
index 29bdba0..c2ce6da 100644
--- a/Source/Tracking/SetProgression.cs
+++ b/Source/Tracking/SetProgression.cs
@@ -11,31 +11,139 @@ namespace Nuclex.Support.Tracking {
   public class SetProgression<ProgressionType> : Progression
     where ProgressionType : Progression {
 
+    /// <summary>Performs common initialization for the public constructors</summary>
+    private SetProgression() {
+      this.childs = new List<ObservedProgression<ProgressionType>>();
+      this.asyncProgressUpdatedDelegate =
+        new ObservedProgression<ProgressionType>.ReportDelegate(asyncProgressUpdated);
+      this.asyncEndedDelegate =
+        new ObservedProgression<ProgressionType>.ReportDelegate(asyncEnded);
+    }
+
     /// <summary>Initializes a new set progression</summary>
-    /// <param name="progressions">Progressions to track with this set</param>
+    /// <param name="childs">Progressions to track with this set</param>
     /// <remarks>
     ///   Uses a default weighting factor of 1.0 for all progressions.
     /// </remarks>
-    public SetProgression(IEnumerable<ProgressionType> progressions) {
+    public SetProgression(IEnumerable<ProgressionType> childs)
+      : this() {
+
+      // Construct a WeightedProgression with the default weight for each
+      // progression and wrap it in an ObservedProgression
+      foreach(ProgressionType progression in childs) {
+        this.childs.Add(
+          new ObservedProgression<ProgressionType>(
+            new WeightedProgression<ProgressionType>(progression),
+            this.asyncProgressUpdatedDelegate, this.asyncEndedDelegate
+          )
+        );
+      }
+
+      // Since all progressions have a weight of 1.0, the total weight is
+      // equal to the number of progressions in our list
+      this.totalWeight = (float)this.childs.Count;
+
     }
 
     /// <summary>Initializes a new set progression</summary>
-    /// <param name="progressions">Progressions to track with this set</param>
-    public SetProgression(IEnumerable<WeightedProgression<ProgressionType>> progressions) {
+    /// <param name="childs">Progressions to track with this set</param>
+    public SetProgression(
+      IEnumerable<WeightedProgression<ProgressionType>> childs
+    )
+      : this() {
+
+      // Construct an ObservedProgression around each of the WeightedProgressions
+      float totalWeight = 0.0f;
+      foreach(WeightedProgression<ProgressionType> progression in childs) {
+        this.childs.Add(
+          new ObservedProgression<ProgressionType>(
+            progression,
+            this.asyncProgressUpdatedDelegate, this.asyncEndedDelegate
+          )
+        );
+
+        // Sum up the total weight
+        totalWeight += progression.Weight;
+      }
+
+      // Take over the summed weight of all progressions we were given
+      this.totalWeight = totalWeight;
+
     }
 
     /// <summary>Childs contained in the progression set</summary>
-    public ReadOnlyCollection<WeightedProgression<ProgressionType>> Childs {
-      get { return null; }
+    public IList<WeightedProgression<ProgressionType>> Childs {
+      get {
+
+        // The wrapper is constructed only when needed. Most of the time, users will
+        // just create a SetProgression and monitor its progress without ever using
+        // the Childs collection.
+        if(this.wrapper == null) {
+
+          // This doesn't need a lock because it's only a stateless wrapper. If it
+          // is constructed twice, then so be it.
+          this.wrapper = new WeightedProgressionWrapperCollection<ProgressionType>(
+            this.childs
+          );
+
+        }
+
+        return this.wrapper;
+
+      }
     }
-/*    
+
+    /// <summary>
+    ///   Called when the progress of one of the observed progressions changes
+    /// </summary>
+    private void asyncProgressUpdated() {
+
+      // Calculate the sum of the progress reported by our child progressions,
+      // scaled to the weight each progression has assigned to it.
+      float totalProgress = 0.0f;
+      for(int index = 0; index < this.childs.Count; ++index) {
+        totalProgress +=
+          this.childs[index].Progress * this.childs[index].WeightedProgression.Weight;
+      }
+
+      // Calculate the actual combined progress
+      if(this.totalWeight > 0.0f)
+        totalProgress /= this.totalWeight;
+
+      // Send out the progress update
+      OnAsyncProgressUpdated(totalProgress);
+
+    }
+
+    /// <summary>
+    ///   Called when an observed progressions ends
+    /// </summary>
+    private void asyncEnded() {
+
+      for(int index = 0; index < this.childs.Count; ++index)
+        if(!this.childs[index].WeightedProgression.Progression.Ended)
+          return;
+
+      OnAsyncEnded();
+
+    }
+
     /// <summary>Progressions being managed in the set</summary>
-    private ReadOnlyCollection<ProgressionType> progressions;
-    /// <summary>whether the progress needs to be recalculated</summary>
-    private volatile bool needProgressRecalculation;
-    /// <summary>Total progress achieved by the progressions in this collection</summary>
-    private volatile float totalProgress;
-*/
+    private List<ObservedProgression<ProgressionType>> childs;
+    /// <summary>
+    ///   Wrapper collection for exposing the child progressions under the
+    ///   WeightedProgression interface
+    /// </summary>
+    private volatile WeightedProgressionWrapperCollection<ProgressionType> wrapper;
+    /// <summary>Summed weight of all progression in the set</summary>
+    private float totalWeight;
+
+    /// <summary>Delegate for the asyncProgressUpdated() method</summary>
+    private ObservedProgression<ProgressionType>.ReportDelegate asyncProgressUpdatedDelegate;
+    /// <summary>Delegate for the asyncEnded() method</summary>
+    private ObservedProgression<ProgressionType>.ReportDelegate asyncEndedDelegate;
+
+
   }
 
 } // namespace Nuclex.Support.Tracking