diff --git a/core/src/com/me/common/ecs/ComponentBag.java b/core/src/com/me/common/ecs/ComponentBag.java
index 88407e4..39b3c0f 100644
--- a/core/src/com/me/common/ecs/ComponentBag.java
+++ b/core/src/com/me/common/ecs/ComponentBag.java
@@ -11,8 +11,8 @@ public class ComponentBag {
     }
 
     public Component get(int index) {
-        if (index > size) {
-            throw new IndexOutOfBoundsException("index > size");
+        if (index >= size) {
+            return null;
         }
         return items[index];
     }
diff --git a/core/src/com/me/common/ecs/ComponentType.java b/core/src/com/me/common/ecs/ComponentType.java
index 6436fba..0fcabbd 100644
--- a/core/src/com/me/common/ecs/ComponentType.java
+++ b/core/src/com/me/common/ecs/ComponentType.java
@@ -50,7 +50,7 @@ public class ComponentType {
     }
 
     protected boolean isTypeInMask(long mask) {
-        return (bits & mask) == mask;
+        return (bits & mask) == bits;
     }
 
     protected static void registerComponentType(Class<? extends Component> component) {
diff --git a/core/src/com/me/common/ecs/Engine.java b/core/src/com/me/common/ecs/Engine.java
index cce1c9f..d24bc4f 100644
--- a/core/src/com/me/common/ecs/Engine.java
+++ b/core/src/com/me/common/ecs/Engine.java
@@ -7,6 +7,10 @@ import com.me.common.ecs.event.Listener;
 public class Engine {
 
     private Array<Entity> entities;
+    private Array<Entity> toActivate;
+    private Array<Entity> toDeactivate;
+    private Array<Entity> toRemove;
+
     private ComponentBag[] components;
     private Array<EntitySystem> systems;
 
@@ -14,6 +18,10 @@ public class Engine {
 
     public Engine() {
         this.entities = new Array<>();
+        this.toActivate = new Array<>();
+        this.toDeactivate = new Array<>();
+        this.toRemove = new Array<>();
+
         this.systems = new Array<>();
         this.listenerRegistry = new ListenerRegistry();
     }
@@ -26,6 +34,10 @@ public class Engine {
         this.systems.add(system);
     }
 
+    public void registerListener(Listener listener) {
+        listenerRegistry.registerListener(listener);
+    }
+
     public void ready() {
         this.components = new ComponentBag[ComponentType.getRegisteredComponentTypeCount()];
         for (int i = 0; i < components.length; i++) {
@@ -33,10 +45,22 @@ public class Engine {
         }
     }
 
+    public Array<Entity> getEntities() {
+        return entities;
+    }
+
+    public int getEntityCount() {
+        return entities.size;
+    }
+
     public void update(float dt) {
+        activatePending();
+        deactivatePending();
+        removePending();
+
         for (EntitySystem system : systems) {
             system.preProcessing();
-            updateSystem(system, dt);
+            system.processEntities(dt);
             system.postProcessing();
         }
     }
@@ -47,13 +71,59 @@ public class Engine {
         return entity;
     }
 
-    public void removeEntity(Entity entity) {
-        removeAllEntityComponents(entity.getId());
-        entities.removeValue(entity, true);
+    protected void removeEntity(Entity entity) {
+        entity.deactivate();
+        toRemove.add(entity);
     }
 
-    public void registerListener(Listener listener) {
-        listenerRegistry.registerListener(listener);
+    private void removePending() {
+        if (toRemove.isEmpty()) {
+            return;
+        }
+
+        for (Entity entity : toRemove) {
+            removeAllEntityComponents(entity.getId());
+            entities.removeValue(entity, true);
+        }
+
+        toRemove.clear();
+    }
+
+    protected void activateEntity(Entity entity) {
+        toActivate.add(entity);
+    }
+
+    private void activatePending() {
+        if (toActivate.isEmpty()) {
+            return;
+        }
+
+        for (Entity entity : toActivate) {
+            for (EntitySystem system : systems) {
+                if (system.interestedIn(entity)) {
+                    system.entities.add(entity);
+                }
+            }
+        }
+        toActivate.clear();
+    }
+
+    protected void deactivateEntity(Entity entity) {
+        toDeactivate.add(entity);
+    }
+
+    private void deactivatePending() {
+        if (toDeactivate.isEmpty()) {
+            return;
+        }
+
+        for (Entity entity : toDeactivate) {
+            for (EntitySystem system : systems) {
+                system.entities.removeValue(entity, true);
+            }
+        }
+
+        toDeactivate.clear();
     }
 
     public void callEvent(Event event) {
@@ -72,6 +142,7 @@ public class Engine {
         entity.addComponentType(type);
     }
 
+
     protected void removeEntityComponent(Entity entity, Component component) {
         ComponentType type = ComponentType.getComponentType(component.getClass());
         components[type.getId()].remove(entity.getId());
@@ -83,21 +154,4 @@ public class Engine {
         return clazz.cast(components[type.getId()].get(entity.getId()));
     }
 
-    protected void updateSystem(EntitySystem system, float dt) {
-        for (Entity entity : entities) {
-            if (!entity.isActive()) {
-                continue;
-            }
-
-            // Check if this system is interested in this entity
-            if ((entity.getComponentBits() & system.getTypeMask()) != system.getTypeMask()) {
-                continue;
-            }
-
-            // If so, process the entity
-            system.processEntity(entity, dt);
-        }
-    }
-
-
 }
diff --git a/core/src/com/me/common/ecs/Entity.java b/core/src/com/me/common/ecs/Entity.java
index 444014c..3645169 100644
--- a/core/src/com/me/common/ecs/Entity.java
+++ b/core/src/com/me/common/ecs/Entity.java
@@ -26,17 +26,27 @@ public final class Entity {
     }
 
     public void activate() {
-        this.active = true;
+        active = true;
+        engine.activateEntity(this);
     }
 
     public void deactivate() {
-        this.active = false;
+        active = false;
+        engine.deactivateEntity(this);
+    }
+
+    public void remove() {
+        engine.removeEntity(this);
     }
 
     public Engine getEngine() {
         return this.engine;
     }
 
+    public boolean hasComponent(Class<? extends Component> clazz) {
+        return ComponentType.getComponentType(clazz).isTypeInMask(componentBits);
+    }
+
     public <T extends Component> T getComponent(Class<T> clazz) {
         return engine.getEntityComponent(this, clazz);
     }
diff --git a/core/src/com/me/common/ecs/EntitySystem.java b/core/src/com/me/common/ecs/EntitySystem.java
index 8a81d08..51f8ecc 100644
--- a/core/src/com/me/common/ecs/EntitySystem.java
+++ b/core/src/com/me/common/ecs/EntitySystem.java
@@ -1,25 +1,36 @@
 package com.me.common.ecs;
 
+import com.badlogic.gdx.utils.Array;
+
 public abstract class EntitySystem {
 
     private long typeBits;
 
+    protected Array<Entity> entities;
+
     public EntitySystem(Class<? extends Component>... components) {
         typeBits = ComponentType.getMaskBits(components);
-    }
-
-    /**
-     * @return the type mask for this system. Only entities containing all component types specified
-     * by the mask will be processed by it.
-     */
-    public long getTypeMask() {
-        return typeBits;
+        entities = new Array<>();
     }
 
     public void preProcessing() {}
 
+    public Array<Entity> getEntities() {
+        return entities;
+    }
+
+    public void processEntities(float dt) {
+        for (int i = 0, n = getEntities().size; i < n; i++) {
+            processEntity(entities.get(i), dt);
+        }
+    }
+
     public abstract void processEntity(Entity entity, float dt);
 
     public void postProcessing() {}
 
+    public boolean interestedIn(Entity entity) {
+        return (entity.getComponentBits() & typeBits) == typeBits;
+    }
+
 }