diff --git a/src/MediatorPattern/MediatorPatternExamples.cs b/src/MediatorPattern/MediatorPatternExamples.cs
index 99f28dc..84a11f5 100644
--- a/src/MediatorPattern/MediatorPatternExamples.cs
+++ b/src/MediatorPattern/MediatorPatternExamples.cs
@@ -13,11 +13,11 @@ namespace MediatorPattern
         {
             Console.WriteLine(GetPatternDescription());
             Console.WriteLine(GetActors());
+            Console.WriteLine(WhenToUseIt());
+            GoToNextStep();
 
-            //GoToNextStep();
-
-            //StockExchangeExample stockExample = new StockExchangeExample();
-            //stockExample.Run();
+            StockExchangeExample stockExample = new StockExchangeExample();
+            stockExample.Run();
 
             GoToNextStep();
             AirTrafficControlExample airTraficExample = new AirTrafficControlExample();
@@ -41,6 +41,16 @@ Colleague: objects that communicate through the mediator
 ";
         }
 
+        static string WhenToUseIt()
+        {
+            return @"When to use it:
+Identify a collection of interacting objects whose interaction needs simplification
+Get a new abstract class that encapsulates that interaction
+Create a instance of that class and redo the interaction with that class alone
+But, don’t play God!
+";
+        }
+
         private static void GoToNextStep()
         {
             Console.ReadKey();
diff --git a/src/MediatorPattern/UserToGroup/Group.cs b/src/MediatorPattern/UserToGroup/Group.cs
new file mode 100644
index 0000000..1ca187d
--- /dev/null
+++ b/src/MediatorPattern/UserToGroup/Group.cs
@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace MediatorPattern.UserToGroup
+{
+    /// <summary>
+    /// Colleague
+    /// </summary>
+    public class Group
+    {
+        public int ID { get; set; }
+    }
+}
diff --git a/src/MediatorPattern/UserToGroup/User.cs b/src/MediatorPattern/UserToGroup/User.cs
new file mode 100644
index 0000000..dbd2e59
--- /dev/null
+++ b/src/MediatorPattern/UserToGroup/User.cs
@@ -0,0 +1,25 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace MediatorPattern.UserToGroup
+{
+    /// <summary>
+    /// Colleague
+    /// </summary>
+    public class User
+    {
+        UsersToGroups usersToGroups;
+        public User(UsersToGroups usersToGroups)
+        {
+            this.usersToGroups = usersToGroups;
+        }
+        public int ID { get; set; }
+
+        public void AddGroup(Group g)
+        {
+            usersToGroups.AddUserToGroup(this, g);
+        }
+    }    
+}
diff --git a/src/MediatorPattern/UserToGroup/UsersToGroups.cs b/src/MediatorPattern/UserToGroup/UsersToGroups.cs
new file mode 100644
index 0000000..49a9778
--- /dev/null
+++ b/src/MediatorPattern/UserToGroup/UsersToGroups.cs
@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace MediatorPattern.UserToGroup
+{
+    /// <summary>
+    /// Mediator
+    /// </summary>
+    public class UsersToGroups
+    {
+        List<Tuple<User, Group>> usersToGroups;
+
+        public UsersToGroups()
+        {
+            usersToGroups = new List<Tuple<User, Group>>();
+            
+        }
+
+        public void AddUserToGroup(User user, Group group)
+        {
+            if (!usersToGroups.Any(ug => ug.Item1.ID == user.ID && ug.Item2.ID == group.ID))
+                usersToGroups.Add(new Tuple<User, Group>(user, group));
+        }
+
+        public void RemoveUserFromGroup(User user, Group group)
+        {
+            usersToGroups.RemoveAll(t => t.Item1.ID == user.ID && t.Item2.ID == group.ID);
+        }
+
+    }
+}