diff --git a/ECS/DataStructures/TypeSafeFasterListForECS.cs b/ECS/DataStructures/TypeSafeFasterListForECS.cs
index 161ecf4..4bca085 100644
--- a/ECS/DataStructures/TypeSafeFasterListForECS.cs
+++ b/ECS/DataStructures/TypeSafeFasterListForECS.cs
@@ -48,12 +48,21 @@ namespace Svelto.ECS.Internal
         {
             var index = this.Count;
             
-            AddRange(entityViewListValue as FasterList<T>);
+            base.AddRange(entityViewListValue as FasterList<T>);
             
             for (int i = index; i < Count; ++i)
                 _mappedIndices[this[i].ID] = i;
         }
 
+        new public void Add(T entityView)
+        {
+            var index = this.Count;
+
+            base.Add(entityView);
+
+            _mappedIndices[entityView.ID] = index;
+        }
+
         public void ReserveCapacity(int capacity)
         {
             if (this.ToArrayFast().Length < capacity)
diff --git a/ECS/EnginesRootEntities.cs b/ECS/EnginesRootEntities.cs
index 923c2bb..f9c3896 100644
--- a/ECS/EnginesRootEntities.cs
+++ b/ECS/EnginesRootEntities.cs
@@ -164,6 +164,45 @@ namespace Svelto.ECS
             InternalRemove(EntityDescriptorTemplate<T>.Default.entityViewsToBuild, entityID, _groupEntityViewsDB[groupID]);
         }
 
+        void SwapEntityGroup<T>(int entityID, int fromGroupID, int toGroupID) where T : IEntityDescriptor, new()
+        {
+            DesignByContract.Check.Require(fromGroupID != toGroupID, "can't move an entity to the same group where it already belongs to");
+
+            var entityViewBuilders = EntityDescriptorTemplate<T>.Default.entityViewsToBuild;
+            int entityViewBuildersCount = entityViewBuilders.Length;
+
+            for (int i = 0; i < entityViewBuildersCount; i++)
+            {
+                IEntityViewBuilder entityViewBuilder = entityViewBuilders[i];
+                Type entityViewType = entityViewBuilder.GetEntityViewType();
+                Dictionary<Type, ITypeSafeList> dictionary = _groupEntityViewsDB[fromGroupID];
+
+                ITypeSafeList fromSafeList = dictionary[entityViewType];
+
+                Dictionary<Type, ITypeSafeList> groupedEntityViewsTyped;
+                if (_groupEntityViewsDB.TryGetValue(toGroupID, out groupedEntityViewsTyped) == false)
+                {
+                    groupedEntityViewsTyped = new Dictionary<Type, ITypeSafeList>();
+
+                    _groupEntityViewsDB.Add(toGroupID, groupedEntityViewsTyped);
+                }
+
+                ITypeSafeList toSafeList;
+
+                if (groupedEntityViewsTyped.TryGetValue(entityViewType, out toSafeList) == false)
+                {
+                    toSafeList = fromSafeList.Create();
+                }
+
+                entityViewBuilder.MoveEntityView(entityID, fromSafeList, toSafeList);
+
+                if (fromSafeList.UnorderedRemove(entityID) == false)
+                    dictionary.Remove(entityViewType);
+
+                if (dictionary.Count == 0) _groupEntityViewsDB.Remove(fromGroupID);
+            }
+        }
+
         void InternalRemove(IEntityViewBuilder[] entityViewBuilders, int entityID,
                     Dictionary<Type, ITypeSafeList> entityViewsDB)
         {
@@ -192,6 +231,13 @@ namespace Svelto.ECS
 
         void InternalRemove(IEntityViewBuilder[] entityViewBuilders, int entityID, int groupID,
                             Dictionary<Type, ITypeSafeList> entityViewsDB)
+        {
+            InternalRemoveFromDB(entityViewBuilders, entityID, groupID);
+
+            InternalRemove(entityViewBuilders, entityID, entityViewsDB);
+        }
+
+        void InternalRemoveFromDB(IEntityViewBuilder[] entityViewBuilders, int entityID, int groupID)
         {
             int entityViewBuildersCount = entityViewBuilders.Length;
 
@@ -205,8 +251,6 @@ namespace Svelto.ECS
 
                 if (dictionary.Count == 0) _groupEntityViewsDB.Remove(groupID);
             }
-
-            InternalRemove(entityViewBuilders, entityID, entityViewsDB);
         }
 
         static void RemoveEntityViewFromEngines(Dictionary<Type, FasterList<IHandleEntityViewEngine>> entityViewEngines,
@@ -297,6 +341,11 @@ namespace Svelto.ECS
                 _weakReference.Target.RemoveEntity<T>(entityID);
             }
 
+            public void SwapEntityGroup<T>(int entityID, int fromGroupID, int toGroupID) where T : IEntityDescriptor, new()
+            {
+                _weakReference.Target.SwapEntityGroup<T>(entityID, fromGroupID, toGroupID);
+            }
+
             readonly DataStructures.WeakReference<EnginesRoot> _weakReference;
         }
 
diff --git a/ECS/EnginesRootSubmission.cs b/ECS/EnginesRootSubmission.cs
index b51f3f2..894881a 100644
--- a/ECS/EnginesRootSubmission.cs
+++ b/ECS/EnginesRootSubmission.cs
@@ -89,9 +89,9 @@ namespace Svelto.ECS
         {
             foreach (var group in groupedEntityViewsToAdd)
             {
-                AddEntityViewsToTheDBAndSuitableEngines(group.Value, entityViewsDB);
-
                 AddEntityViewsToGroupDB(groupEntityViewsDB, @group);
+
+                AddEntityViewsToTheDBAndSuitableEngines(group.Value, entityViewsDB);
             }
         }
 
diff --git a/ECS/EntityDescriptorTemplate.cs b/ECS/EntityDescriptor.cs
similarity index 98%
rename from ECS/EntityDescriptorTemplate.cs
rename to ECS/EntityDescriptor.cs
index d917577..91e09aa 100644
--- a/ECS/EntityDescriptorTemplate.cs
+++ b/ECS/EntityDescriptor.cs
@@ -105,7 +105,7 @@ namespace Svelto.ECS.Internal
             }
         }
 
-        static IEntityView BuildEntityView(int entityID, Dictionary<Type, ITypeSafeList> entityViewsByType,
+        internal static IEntityView BuildEntityView(int entityID, Dictionary<Type, ITypeSafeList> entityViewsByType,
                                                  Type entityViewType, IEntityViewBuilder entityViewBuilder)
         {
             ITypeSafeList entityViewsList;
diff --git a/ECS/EntityViewBuilder.cs b/ECS/EntityViewBuilder.cs
index 6b02a66..b512cf9 100644
--- a/ECS/EntityViewBuilder.cs
+++ b/ECS/EntityViewBuilder.cs
@@ -9,6 +9,7 @@ namespace Svelto.ECS
         ITypeSafeList Preallocate(ref ITypeSafeList list, int size);
 
         Type GetEntityViewType();
+        void MoveEntityView(int entityID, ITypeSafeList fromSafeList, ITypeSafeList toSafeList);
     }
 
     public class EntityViewBuilder<EntityViewType> : IEntityViewBuilder where EntityViewType : EntityView, new()
@@ -42,6 +43,14 @@ namespace Svelto.ECS
             return _entityViewType;
         }
 
+        public void MoveEntityView(int entityID, ITypeSafeList fromSafeList, ITypeSafeList toSafeList)
+        {
+            var fromCastedList = fromSafeList as TypeSafeFasterListForECSForClasses<EntityViewType>;
+            var toCastedList = toSafeList as TypeSafeFasterListForECSForClasses<EntityViewType>;
+
+            toCastedList.Add(fromCastedList[entityID]);
+        }
+
         readonly Type _entityViewType = typeof(EntityViewType);
     }
 
@@ -77,6 +86,14 @@ namespace Svelto.ECS
             return _entityViewType;
         }
 
+        public void MoveEntityView(int entityID, ITypeSafeList fromSafeList, ITypeSafeList toSafeList)
+        {
+            var fromCastedList = fromSafeList as TypeSafeFasterListForECSForStructs<EntityViewType>;
+            var toCastedList = toSafeList as TypeSafeFasterListForECSForStructs<EntityViewType>;
+
+            toCastedList.Add(fromCastedList[entityID]);
+        }
+
         readonly Type _entityViewType = typeof(EntityViewType);
     }    
 }
\ No newline at end of file
diff --git a/ECS/IEnginesInterfaces.cs b/ECS/IEnginesInterfaces.cs
index 1929ca9..fe0494b 100644
--- a/ECS/IEnginesInterfaces.cs
+++ b/ECS/IEnginesInterfaces.cs
@@ -16,11 +16,12 @@ namespace Svelto.ECS
     public interface IEntityFunctions
     {
         void RemoveEntity(int entityID, IRemoveEntityComponent removeInfo);
-
         void RemoveEntity<T>(int entityID) where T:IEntityDescriptor, new();
-        
+
         void RemoveMetaEntity<T>(int metaEntityID) where T:IEntityDescriptor, new();
 
         void RemoveEntityFromGroup<T>(int entityID, int groupID) where T:IEntityDescriptor, new();
+
+        void SwapEntityGroup<T>(int entityID, int fromGroupID, int toGroupID) where T : IEntityDescriptor, new();
     }
 }