diff --git a/xunit.runner.wpf/ITestUtil.cs b/xunit.runner.wpf/ITestUtil.cs
index eaca6a5..f0bae10 100644
--- a/xunit.runner.wpf/ITestUtil.cs
+++ b/xunit.runner.wpf/ITestUtil.cs
@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Linq;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using System.Windows.Threading;
 using xunit.runner.data;
@@ -20,7 +21,7 @@ namespace xunit.runner.wpf
         /// <summary>
         /// Begin a run of a unit test for the given assembly.
         /// </summary>
-        ITestRunSession Run(Dispatcher dispatcher, string assemblyPath);
+        ITestRunSession Run(Dispatcher dispatcher, string assemblyPath, CancellationToken cancellationToken = default(CancellationToken));
     }
 
     internal sealed class TestResultEventArgs : EventArgs
@@ -37,6 +38,16 @@ namespace xunit.runner.wpf
 
     internal interface ITestRunSession
     {
+        bool IsRunning { get; }
+
+        /// <summary>
+        /// Raised when an idividual test is finished running.
+        /// </summary>
         event EventHandler<TestResultEventArgs> TestFinished;
+
+        /// <summary>
+        /// Raised when the session has finished executing all of the specified tests.
+        /// </summary>
+        event EventHandler SessionFinished;
     }
 }
diff --git a/xunit.runner.wpf/Impl/RemoteTestUtil .BackgroundRunner.cs b/xunit.runner.wpf/Impl/RemoteTestUtil .BackgroundRunner.cs
index 9ac17ec..cf09a58 100644
--- a/xunit.runner.wpf/Impl/RemoteTestUtil .BackgroundRunner.cs	
+++ b/xunit.runner.wpf/Impl/RemoteTestUtil .BackgroundRunner.cs	
@@ -6,6 +6,7 @@ using System.IO;
 using System.IO.Pipes;
 using System.Linq;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using xunit.runner.data;
 using xunit.runner.wpf.ViewModel;
@@ -18,11 +19,13 @@ namespace xunit.runner.wpf.Impl
         {
             private readonly ConcurrentQueue<TestResultData> _resultQueue;
             private readonly BinaryReader _reader;
+            private readonly CancellationToken _cancellationToken;
 
-            internal BackgroundRunner(ConcurrentQueue<TestResultData> resultQueue, BinaryReader reader)
+            internal BackgroundRunner(ConcurrentQueue<TestResultData> resultQueue, BinaryReader reader, CancellationToken cancellationToken)
             {
                 _resultQueue = resultQueue;
                 _reader = reader;
+                _cancellationToken = cancellationToken;
             }
 
             /// <summary>
@@ -32,7 +35,7 @@ namespace xunit.runner.wpf.Impl
             /// <returns></returns>
             internal Task GoOnBackground()
             {
-                while (true)
+                while (!_cancellationToken.IsCancellationRequested)
                 {
                     TestResultData result;
                     try
diff --git a/xunit.runner.wpf/Impl/RemoteTestUtil .RunSession.cs b/xunit.runner.wpf/Impl/RemoteTestUtil .RunSession.cs
index cc0ca7d..53ec4ad 100644
--- a/xunit.runner.wpf/Impl/RemoteTestUtil .RunSession.cs	
+++ b/xunit.runner.wpf/Impl/RemoteTestUtil .RunSession.cs	
@@ -24,6 +24,7 @@ namespace xunit.runner.wpf.Impl
             private readonly DispatcherTimer _timer;
             private bool _closed;
             private event EventHandler<TestResultEventArgs> _testFinished;
+            private event EventHandler _sessionFinished;
 
             internal RunSession(Connection connection, Dispatcher dispatcher, ConcurrentQueue<TestResultData> resultQueue)
             {
@@ -58,16 +59,26 @@ namespace xunit.runner.wpf.Impl
                 _closed = true;
                 _timer.Stop();
                 ((IDisposable)_connection).Dispose();
+
+                _sessionFinished?.Invoke(this, EventArgs.Empty);
             }
 
             #region ITestRunSession
 
+            bool ITestRunSession.IsRunning => !_closed;
+
             event EventHandler<TestResultEventArgs> ITestRunSession.TestFinished
             {
                 add { _testFinished += value; }
                 remove { _testFinished -= value; }
             }
 
+            event EventHandler ITestRunSession.SessionFinished
+            {
+                add { _sessionFinished += value; }
+                remove { _sessionFinished -= value; }
+            }
+
             #endregion
         }
     }
diff --git a/xunit.runner.wpf/Impl/RemoteTestUtil.cs b/xunit.runner.wpf/Impl/RemoteTestUtil.cs
index 264fb71..9275f82 100644
--- a/xunit.runner.wpf/Impl/RemoteTestUtil.cs
+++ b/xunit.runner.wpf/Impl/RemoteTestUtil.cs
@@ -6,6 +6,7 @@ using System.IO;
 using System.IO.Pipes;
 using System.Linq;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using System.Windows.Threading;
 using xunit.runner.data;
@@ -53,6 +54,8 @@ namespace xunit.runner.wpf.Impl
             var processStartInfo = new ProcessStartInfo();
             processStartInfo.FileName = typeof(xunit.runner.worker.Program).Assembly.Location;
             processStartInfo.Arguments = $"{action} {argument}";
+            processStartInfo.WindowStyle = ProcessWindowStyle.Hidden;
+
             var process = Process.Start(processStartInfo);
             try
             {
@@ -99,11 +102,11 @@ namespace xunit.runner.wpf.Impl
             return list;
         }
 
-        private RunSession Run(Dispatcher dispatcher, string assemblyPath)
+        private RunSession Run(Dispatcher dispatcher, string assemblyPath, CancellationToken cancellationToken)
         {
             var connection = StartWorkerProcess(Constants.ActionRun, assemblyPath);
             var queue = new ConcurrentQueue<TestResultData>();
-            var backgroundRunner = new BackgroundRunner(queue, new BinaryReader(connection.Stream, Constants.Encoding, leaveOpen: true));
+            var backgroundRunner = new BackgroundRunner(queue, new BinaryReader(connection.Stream, Constants.Encoding, leaveOpen: true), cancellationToken);
             Task.Run(backgroundRunner.GoOnBackground);
 
             return new RunSession(connection, dispatcher, queue);
@@ -116,9 +119,9 @@ namespace xunit.runner.wpf.Impl
             return Discover(assemblyPath);
         }
 
-        ITestRunSession ITestUtil.Run(Dispatcher dispatcher, string assemblyPath)
+        ITestRunSession ITestUtil.Run(Dispatcher dispatcher, string assemblyPath, CancellationToken cancellationToken)
         {
-            return Run(dispatcher, assemblyPath);
+            return Run(dispatcher, assemblyPath, cancellationToken);
         }
 
         #endregion
diff --git a/xunit.runner.wpf/ViewModel/MainViewModel.cs b/xunit.runner.wpf/ViewModel/MainViewModel.cs
index cf0bcea..9649805 100644
--- a/xunit.runner.wpf/ViewModel/MainViewModel.cs
+++ b/xunit.runner.wpf/ViewModel/MainViewModel.cs
@@ -25,8 +25,10 @@ namespace xunit.runner.wpf.ViewModel
         private readonly ObservableCollection<TestCaseViewModel> allTestCases = new ObservableCollection<TestCaseViewModel>();
         private CancellationTokenSource filterCancellationTokenSource = new CancellationTokenSource();
 
+        private List<ITestRunSession> testRunSessionList = new List<ITestRunSession>();
+        private CancellationTokenSource cancellationTokenSource;
         private bool isBusy;
-        private bool isCancelRequested;
+
         public MainViewModel()
         {
             if (IsInDesignMode)
@@ -205,16 +207,6 @@ namespace xunit.runner.wpf.ViewModel
             }
         }
 
-        private bool IsCancelRequested
-        {
-            get { return isCancelRequested; }
-            set
-            {
-                isCancelRequested = value;
-                CancelCommand.RaiseCanExecuteChanged();
-            }
-        }
-
         private static void OnExecuteExit()
         {
             Application.Current.Shutdown();
@@ -227,7 +219,6 @@ namespace xunit.runner.wpf.ViewModel
         {
             try
             {
-                IsBusy = true;
                 TestsCompleted = 0;
                 TestsPassed = 0;
                 TestsFailed = 0;
@@ -239,24 +230,47 @@ namespace xunit.runner.wpf.ViewModel
             {
                 MessageBox.Show(ex.ToString());
             }
-            finally
-            {
-                IsBusy = false;
-                IsCancelRequested = false;
-            }
         }
 
         private void RunTests()
         {
+            Debug.Assert(this.cancellationTokenSource == null);
+            Debug.Assert(this.testRunSessionList.Count == 0);
+
             foreach (var tc in TestCases)
             {
                 tc.State = TestState.NotRun;
             }
 
-            // Hacky way of using one assembly for now.  Will expand later. 
-            var assemblyPath = TestCases.Select(x => x.AssemblyFileName).First();
-            var session = this.testUtil.Run(Dispatcher.CurrentDispatcher, assemblyPath);
-            session.TestFinished += OnTestFinished;
+            // TODO: Need a way to filter based on traits, selected test cases, etc ...  For now we just run
+            // everything. 
+
+            this.cancellationTokenSource = new CancellationTokenSource();
+            foreach (var assemblyPath in TestCases.Select(x => x.AssemblyFileName).Distinct())
+            {
+                var session = this.testUtil.Run(Dispatcher.CurrentDispatcher, assemblyPath, this.cancellationTokenSource.Token);
+                session.TestFinished += OnTestFinished;
+                session.SessionFinished += delegate { OnTestRunSessionFinished(session); };
+                this.testRunSessionList.Add(session);
+            }
+
+            this.IsBusy = true;
+            this.RunCommand.RaiseCanExecuteChanged();
+            this.CancelCommand.RaiseCanExecuteChanged();
+        }
+
+        private void OnTestRunSessionFinished(ITestRunSession session)
+        {
+            Debug.Assert(this.testRunSessionList.Contains(session));
+            this.testRunSessionList.Remove(session);
+
+            if (this.testRunSessionList.Count == 0)
+            {
+                this.cancellationTokenSource = null;
+                this.IsBusy = false;
+                this.RunCommand.RaiseCanExecuteChanged();
+                this.CancelCommand.RaiseCanExecuteChanged();
+            }
         }
 
         private void OnTestFinished(object sender, TestResultEventArgs e)
@@ -284,11 +298,15 @@ namespace xunit.runner.wpf.ViewModel
             }
         }
 
-        private bool CanExecuteCancel() => IsBusy && !IsCancelRequested;
+        private bool CanExecuteCancel()
+        {
+            return this.cancellationTokenSource != null && !this.cancellationTokenSource.IsCancellationRequested;
+        }
 
         private void OnExecuteCancel()
         {
-            this.IsCancelRequested = true;
+            Debug.Assert(CanExecuteCancel());
+            this.cancellationTokenSource.Cancel();
         }
 
         public bool IsPassedFilterChecked