diff --git a/Sharpasonne/Engine.cs b/Sharpasonne/Engine.cs
index 83b3d29..37a4953 100644
--- a/Sharpasonne/Engine.cs
+++ b/Sharpasonne/Engine.cs
@@ -10,29 +10,32 @@
 
 namespace Sharpasonne
 {
+    using IRuleMap = IImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>>;
+    using RuleMap = ImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>>;
+
     // TODO: Consider rename.
     public class Engine : IEngine
     {
-        public Board Board { get; } = new Board();
+        public Board Board { get; }
 
-        /// <summary>
-        /// Players collection for managing player stats and turns.
-        /// </summary>
+        /// <inheritdoc />
         public Players Players { get; }
 
-        /// <summary>
-        /// 1-index number of the player who's turn it is to play an action.
-        /// </summary>
+        /// <inheritdoc />
         public int CurrentPlayerTurn { get; } = 1;
 
-        public IImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>> Rules { get; }
-            = ImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>>.Empty;
+        /// <summary>
+        /// Map of IGameAction to rules that apply to that IGameAction.
+        /// Keys must be assignable from IGameAction.
+        /// </summary>
+        /// <remarks>Type system can't enforce this itself.</remarks>
+        public IRuleMap Rules { get; } = RuleMap.Empty;
 
         /// <summary>Attempts to create a Game engine.</summary>
         /// <param name="gameActions"></param>
         /// <param name="rules">Must provide list for every action to be used by
         /// Perform.</param>
-        /// <param name="gameActions"></param>
+        /// <returns>None if any key of <paramref name="rules"/> is not an <see cref="IGameAction"/>.</returns>
         public static Option<Engine, Exception> Create(
             [NotNull] IImmutableQueue<IGameAction>                                   gameActions,
             [NotNull] IImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>> rules,
@@ -49,24 +52,31 @@ public static Option<Engine, Exception> Create(
                 return Option.None<Engine, Exception>(new ArgumentOutOfRangeException(nameof(gameActions), message));
             }
 
-            return Option.Some<Engine, Exception>(new Engine(gameActions, rules, players));
+            return Option.Some<Engine, Exception>(new Engine(gameActions, rules, players, new Board()));
         }
 
         private Engine(
             [NotNull] IImmutableQueue<IGameAction>                                   gameActions,
             [NotNull] IImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>> rules,
-            [NotNull] Players                                                        players)
+            [NotNull] Players                                                        players,
+            [NotNull] Board                                                          board,
+                      int                                                            currentPlayerTurn = 1)
         {
-            this.Rules = rules;
-            this.Players = players;
+            this.Rules             = rules;
+            this.Players           = players;
+            this.Board             = board;
+            this.CurrentPlayerTurn = currentPlayerTurn;
         }
 
-        private Engine(IEngine engine)
+        private static Engine NextTurn(IEngine engine)
         {
-            this.Board = engine.Board;
-            this.Rules = engine.Rules;
-            this.Players = engine.Players;
-            this.CurrentPlayerTurn = engine.Players.NextPlayer(engine.CurrentPlayerTurn);
+            var nextTurn = new Engine(ImmutableQueue<IGameAction>.Empty,
+                engine.Rules,
+                engine.Players,
+                engine.Board,
+                engine.Players.NextPlayer(engine.CurrentPlayerTurn));
+
+            return nextTurn;
         }
 
         public Optional.Option<Engine, IEnumerable<string>> Perform(
@@ -84,7 +94,7 @@ public Optional.Option<Engine, IEnumerable<string>> Perform(
                 return Option.None<Engine, IEnumerable<string>>(new string[] {});
             }
 
-            var newEngine = new Engine(action.Perform(this));
+            var newEngine = Engine.NextTurn(action.Perform(this));
 
             return Option.Some<Engine, IEnumerable<string>>(newEngine);
         }
diff --git a/Sharpasonne/GameActions/EngineState.cs b/Sharpasonne/GameActions/EngineState.cs
index 0c011aa..1d3bdd4 100644
--- a/Sharpasonne/GameActions/EngineState.cs
+++ b/Sharpasonne/GameActions/EngineState.cs
@@ -5,7 +5,13 @@
 
 namespace Sharpasonne.GameActions
 {
-    public class EngineState : IEngine
+    using IRuleMap = IImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>>;
+
+    /// <summary>
+    /// Is the state of an engine without any functionality, because an Engine
+    /// cannot be constructed from the outside with this state.
+    /// </summary>
+    internal class EngineState : IEngine
     {
         public EngineState(Board board, IEngine engine)
         {
@@ -15,9 +21,9 @@ public EngineState(Board board, IEngine engine)
             this.CurrentPlayerTurn = engine.CurrentPlayerTurn;
         }
 
-        public Board                                                          Board             { get; }
-        public Players                                                        Players           { get; }
-        public int                                                            CurrentPlayerTurn { get; }
-        public IImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>> Rules             { get; }
+        public Board    Board             { get; }
+        public Players  Players           { get; }
+        public int      CurrentPlayerTurn { get; }
+        public IRuleMap Rules             { get; }
     }
 }
\ No newline at end of file
diff --git a/Sharpasonne/GameActions/IGameAction.cs b/Sharpasonne/GameActions/IGameAction.cs
index 1856c7b..ba15e4d 100644
--- a/Sharpasonne/GameActions/IGameAction.cs
+++ b/Sharpasonne/GameActions/IGameAction.cs
@@ -1,5 +1,8 @@
 namespace Sharpasonne.GameActions
 {
+    /// <summary>
+    /// A command to change the state of the game.
+    /// </summary>
     public interface IGameAction
     {
         IEngine Perform(IEngine engine);
diff --git a/Sharpasonne/IEngine.cs b/Sharpasonne/IEngine.cs
index 8e9cb37..16cf07c 100644
--- a/Sharpasonne/IEngine.cs
+++ b/Sharpasonne/IEngine.cs
@@ -9,8 +9,17 @@ namespace Sharpasonne
     public interface IEngine
     {
         Board Board { get; }
+
+        /// <summary>
+        /// Players collection for managing player stats and turns.
+        /// </summary>
         Players Players { get; }
+
+        /// <summary>
+        /// 1-index number of the player who's turn it is to play an action.
+        /// </summary>
         int CurrentPlayerTurn { get; }
+
         IImmutableDictionary<Type, IImmutableList<IRule<IGameAction>>> Rules { get; }
     }
 }
diff --git a/Sharpasonne/Rules/AdjacentFeaturesMatchRule.cs b/Sharpasonne/Rules/AdjacentFeaturesMatchRule.cs
index 0cacbf6..418e05a 100644
--- a/Sharpasonne/Rules/AdjacentFeaturesMatchRule.cs
+++ b/Sharpasonne/Rules/AdjacentFeaturesMatchRule.cs
@@ -6,6 +6,10 @@
 
 namespace Sharpasonne.Rules
 {
+    /// <summary>
+    /// Ensures that the type of features on all edges of the tile to place
+    /// match the corresponding features on the surrounding tiles.
+    /// </summary>
     public class AdjacentFeaturesMatchRule : IRule<PlaceTileGameAction>
     {
         public bool Verify<T1>(IEngine engine, T1 action)
@@ -13,14 +17,16 @@ public bool Verify<T1>(IEngine engine, T1 action)
         {
             var adjacent = engine.Board.GetAdjecentTiles(action.Point);
             var allMatch = adjacent
-                .Where(o => o.Value.HasValue)
-                .Select(o => (
-                    o.Key,
-                    o.Value.ValueOrFailure()
+                // Where orientation has a Placement
+                .Where(kv => kv.Value.HasValue)
+                .Select(kv => (
+                    kv.Key,
+                    // Never failure due to Where.
+                    kv.Value.ValueOrFailure() 
                 ))
-                .All(o =>
+                .All(kv =>
                 {
-                    (var direction, var placement) = o;
+                    (var direction, var placement) = kv;
 
                     switch (direction)
                     {
@@ -61,6 +67,10 @@ public bool Verify<T1>(IEngine engine, T1 action)
             return allMatch;
         }
 
+        /// <summary>
+        /// Checks that the order of the types implementing <see cref="IFeatures"/> 
+        /// are aligned, thereby showing that the edges are matched.
+        /// </summary>
         protected bool EdgesMatch(
             IFeature[] from,
             IFeature[] to
diff --git a/Sharpasonne/Rules/HasAdjacentTileRule.cs b/Sharpasonne/Rules/HasAdjacentTileRule.cs
index 7e51fc9..7caf0b0 100644
--- a/Sharpasonne/Rules/HasAdjacentTileRule.cs
+++ b/Sharpasonne/Rules/HasAdjacentTileRule.cs
@@ -3,6 +3,10 @@
 
 namespace Sharpasonne.Rules
 {
+    /// <summary>
+    /// Verify that the <see cref="PlaceTileGameAction"/> will place a tile
+    /// adjacent to a pre-existing tile.
+    /// </summary>
     public class HasAdjacentTileRule : IRule<PlaceTileGameAction>
     {
         public bool Verify<T1>(IEngine engine, T1 gameAction) where T1 : PlaceTileGameAction