diff --git a/main.lua b/main.lua
index cd13075..dad60e1 100644
--- a/main.lua
+++ b/main.lua
@@ -22,20 +22,49 @@ local test_comp_3 = Concord.component("test_comp_3", function(e, b)
 end)
 
 local test_system = Concord.system({Component.test_comp_1})
-function test_system:update(dt)
-    print(#self.pool)
+
+function onEntityAdded(e)
+    print("Added")
 end
 
+function onEntityRemoved(e)
+    print("Removed")
+end
+
+function test_system:init()
+    self.pool.onEntityAdded = onEntityAdded
+    self.pool.onEntityRemoved = onEntityRemoved
+end
+
+function test_system:update(dt)
+    --print(#self.pool)
+end
+
+
+
 local world = Concord.world()
 
 local entity = Concord.entity()
-entity:give(Component.test_comp_2, 100, 100)
-entity:apply()
+entity:give(Component.test_comp_1, 100, 100)
 
 world:addEntity(entity)
 
 world:addSystem(test_system(), "update")
 
 function love.update(dt)
+    world:flush()
+
     world:emit("update", dt)
+end
+
+function love.keypressed(key)
+    if key == "q" then
+        entity:remove(Component.test_comp_1)
+    end
+    if key == "w" then
+        entity:give(Component.test_comp_1)
+    end
+    if key == "e" then
+        world:removeEntity(entity)
+    end
 end
\ No newline at end of file
diff --git a/src/component.lua b/src/component.lua
index 5777743..102e722 100644
--- a/src/component.lua
+++ b/src/component.lua
@@ -51,4 +51,4 @@ return setmetatable(Component, {
    __call = function(_, ...)
       return Component.new(...)
    end,
-})
+})                                                                                                                                                
\ No newline at end of file
diff --git a/src/entity.lua b/src/entity.lua
index 62d64c4..a6c6b29 100644
--- a/src/entity.lua
+++ b/src/entity.lua
@@ -3,7 +3,6 @@
 local PATH = (...):gsub('%.[^%.]+$', '')
 
 local Type = require(PATH..".type")
-local List = require(PATH..".list")
 
 local Entity = {}
 Entity.__index = Entity
@@ -12,8 +11,11 @@ Entity.__index = Entity
 -- @return A new Entity
 function Entity.new()
    local e = setmetatable({
-      removed   = {},
-      worlds = List(),
+      world = nil,
+
+      __isDirty    = true,
+      __wasAdded   = false,
+      __wasRemoved = false,
 
       __isEntity = true,
    }, Entity)
@@ -25,7 +27,13 @@ local function give(e, component, ...)
    local comp = component:__initialize(...)
    e[component] = comp
 
-   e:mark()
+   e.__isDirty = true
+end
+
+local function remove(e, component)
+   e[component] = nil
+
+   e.__isDirty = true
 end
 
 --- Gives an Entity a component with values.
@@ -37,10 +45,6 @@ function Entity:give(component, ...)
       error("bad argument #1 to 'Entity:give' (Component expected, got "..type(component)..")", 2)
    end
 
-   if self[component] then
-      self:remove(component):apply()
-   end
-
    give(self, component, ...)
 
    return self
@@ -68,9 +72,7 @@ function Entity:remove(component)
       error("bad argument #1 to 'Entity:remove' (Component expected, got "..type(component)..")")
    end
 
-   self.removed[#self.removed + 1] = component
-
-   self:mark()
+   remove(self, component)
 
    return self
 end
@@ -85,28 +87,11 @@ function Entity:assemble(assemblage, ...)
    return self
 end
 
-function Entity:mark()
-   for i = 1, self.worlds.size do
-      self.worlds:get(i):markEntity(self)
-   end
-end
-
-function Entity:apply()
-   for i = 1, #self.removed do
-      local component = self.removed[i]
-
-      self[component] = nil
-      self.removed[i] = nil
-   end
-
-   return self
-end
-
 --- Destroys the Entity.
 -- @return self
 function Entity:destroy()
-   for i = 1, self.worlds.size do
-      self.worlds:get(i):removeEntity(self)
+   if self.world then
+      self.world:removeEntity(self)
    end
 
    return self
diff --git a/src/list.lua b/src/list.lua
index a79d20e..16819da 100644
--- a/src/list.lua
+++ b/src/list.lua
@@ -73,7 +73,7 @@ end
 -- @param obj The object to search for
 -- true if the list has the object, false otherwise
 function List:has(obj)
-   return self[obj] and true
+   return self[obj] and true or false
 end
 
 return setmetatable(List, {
diff --git a/src/pool.lua b/src/pool.lua
index 779efd9..e82735a 100644
--- a/src/pool.lua
+++ b/src/pool.lua
@@ -14,9 +14,6 @@ Pool.__index = Pool
 function Pool.new(name, filter)
    local pool = setmetatable(List(), Pool)
 
-   pool.added   = {}
-   pool.removed = {}
-
    pool.name   = name
    pool.filter = filter
 
@@ -25,18 +22,12 @@ function Pool.new(name, filter)
    return pool
 end
 
-function Pool:flush()
-   for i = 1, math.max(#self.added, #self.removed) do
-      self.added[i], self.removed[i] = nil, nil
-   end
-end
-
 --- Checks if an Entity is eligible for the Pool.
 -- @param e The Entity to check
 -- @return True if the entity is eligible, false otherwise
 function Pool:eligible(e)
    for _, component in ipairs(self.filter) do
-      if not e[component] or e.removed[component] then
+      if not e[component] then
          return false
       end
    end
@@ -44,6 +35,22 @@ function Pool:eligible(e)
    return true
 end
 
+function Pool:add(e)
+   List.add(self, e)
+   self:onEntityAdded(e)
+end
+
+function Pool:remove(e)
+   List.remove(self, e)
+   self:onEntityRemoved(e)
+end
+
+function Pool:onEntityAdded(e)
+end
+
+function Pool:onEntityRemoved(e)
+end
+
 return setmetatable(Pool, {
    __index = List,
    __call  = function(_, ...)
diff --git a/src/system.lua b/src/system.lua
index 10729da..b078a50 100644
--- a/src/system.lua
+++ b/src/system.lua
@@ -9,7 +9,6 @@ System.mt    = {
    __index = System,
    __call  = function(systemProto, ...)
       local system = setmetatable({
-         __all   = {},
          __pools = {},
          __world = nil,
 
@@ -63,22 +62,15 @@ end
 
 --- Checks and applies an Entity to the System's pools.
 -- @param e The Entity to check
--- @return True if the Entity was added, false if it was removed. Nil if nothing happend
-function System:__check(e)
+function System:__evaluate(e)
    for _, pool in ipairs(self.__pools) do
-      local poolHas  = pool:has(e)
+      local has  = pool:has(e)
       local eligible = pool:eligible(e)
 
-      if not poolHas and eligible then
+      if not has and eligible then
          pool:add(e)
-         pool.added[#pool.added + 1] = e
-
-         self:__tryAdd(e)
-      elseif poolHas and not eligible then
+      elseif has and not eligible then
          pool:remove(e)
-         pool.removed[#pool.removed + 1] = e
-
-         self:__tryRemove(e)
       end
    end
 end
@@ -86,46 +78,16 @@ end
 --- Remove an Entity from the System.
 -- @param e The Entity to remove
 function System:__remove(e)
-   if self.__all[e] then
-      for _, pool in ipairs(self.__pools) do
-         if pool:has(e) then
-            pool:remove(e)
-            pool.removed[#pool.removed + 1] = e
-         end
-      end
-
-      self.__all[e] = nil
-   end
-end
-
---- Tries to add an Entity to the System.
--- @param e The Entity to add
-function System:__tryAdd(e)
-   if not self.__all[e] then
-      self.__all[e] = 0
-   end
-
-   self.__all[e] = self.__all[e] + 1
-end
-
---- Tries to remove an Entity from the System.
--- @param e The Entity to remove
-function System:__tryRemove(e)
-   if self.__all[e] then
-      self.__all[e] = self.__all[e] - 1
-
-      if self.__all[e] == 0 then
-         self.__all[e] = nil
+   for _, pool in ipairs(self.__pools) do
+      if pool:has(e) then
+         pool:remove(e)
       end
    end
 end
 
-function System:flush() -- luacheck: ignore
-end
-
 function System:clear()
    for i = 1, #self.__pools do
-      self.__pools[i]:flush()
+      self.__pools[i]:clear()
    end
 end
 
@@ -142,7 +104,7 @@ end
 
 -- Default callback for when the System is added to an World.
 -- @param world The World the System was added to
-function System:addedTo(World) -- luacheck: ignore
+function System:addedTo(world) -- luacheck: ignore
 end
 
 -- Default callback for when a System's callback is enabled.
diff --git a/src/world.lua b/src/world.lua
index 59305fa..2712cb6 100644
--- a/src/world.lua
+++ b/src/world.lua
@@ -16,8 +16,8 @@ function World.new()
       systems  = List(),
       events   = {},
 
-      marked   = {},
-      removed  = {},
+      __added   = {},
+      __removed = {},
 
       __isWorld = true,
    }, World)
@@ -33,16 +33,19 @@ function World:addEntity(e)
       error("bad argument #1 to 'World:addEntity' (Entity expected, got "..type(e)..")", 2)
    end
 
-   self:onEntityAdded(e)
+   if e.world then
+      error("bad argument #1 to 'World:addEntity' (Entity was already added to a world)", 2)
+   end
+
+   e.world = self
+   e.__wasAdded = true
 
-   e.worlds:add(self)
    self.entities:add(e)
-   self:checkEntity(e)
 
    return self
 end
 
---- Marks an Entity as removed from the World.
+--- Removes an entity from the World.
 -- @param e The Entity to mark
 -- @return self
 function World:removeEntity(e)
@@ -50,73 +53,46 @@ function World:removeEntity(e)
       error("bad argument #1 to 'World:removeEntity' (Entity expected, got "..type(e)..")", 2)
    end
 
-   self.removed[#self.removed + 1] = e
+   e.__wasRemoved = true
 
    return self
 end
 
-function World:markEntity(e)
-   if not Type.isEntity(e) then
-      error("bad argument #1 to 'World:markEntity' (Entity expected, got "..type(e)..")", 2)
-   end
-
-   self.marked[#self.marked + 1] = e
-
-   return self
-end
-
---- Checks an Entity against all the systems in the World.
--- @param e The Entity to check
--- @return self
-function World:checkEntity(e)
-   if not Type.isEntity(e) then
-      error("bad argument #1 to 'World:checkEntity' (Entity expected, got "..type(e)..")", 2)
-   end
-
-   for i = 1, self.systems.size do
-      self.systems:get(i):__check(e)
-   end
-
-   return self
-end
-
---- Completely removes all marked Entities in the World.
 -- @return self
 function World:flush()
-   while #self.marked > 0 do
-      local marked = self.removed
-      self.removed  = {}
+   local e
+   for i = 1, self.entities.size do
+      e = self.entities:get(i)
 
-      for i = 1, #marked do
-         local e = marked[i]
+      if e.__wasAdded then
+         e.__wasAdded = false
+         e.__isDirty = false
 
-         e.Worlds:apply()
-         e.Worlds:checkEntity(e)
-      end
-   end
-
-   while #self.removed > 0 do
-      local removed = self.removed
-      self.removed  = {}
-
-      for i = 1, #removed do
-         local e = removed[i]
-
-         e.worlds:remove(self)
-         self.entities:remove(e)
-
-         for j = 1, self.systems.size do
-            self.systems:get(j):__remove(e)
+         for i = 1, self.systems.size do
+            self.systems:get(i):__evaluate(e)
          end
 
-         self:onEntityRemoved(e)
+         self:onEntityAdded(e)
       end
-   end
 
-   for i = 1, self.systems.size do
-      local system = self.systems:get(i)
-      system:flush()
-      system:clear()
+      if e.__wasRemoved then
+         e.world = nil
+         self.entities:remove(e)
+
+         for i = 1, self.systems.size do
+            self.systems:get(i):__remove(e)
+         end
+
+         e.__wasRemoved = false
+      end
+
+      if e.__isDirty then
+         for i = 1, self.systems.size do
+            self.systems:get(i):__evaluate(e)
+         end
+
+         e.__isDirty = false
+      end
    end
 
    return self
@@ -142,6 +118,10 @@ function World:addSystem(system, eventName, callback, enabled)
       system.__World = self
 
       system:addedTo(self)
+
+      for i = 1, self.entities.size do
+         system:__evaluate(self.entities:get(i))
+      end
    end
 
    if eventName then
@@ -159,13 +139,6 @@ function World:addSystem(system, eventName, callback, enabled)
       end
    end
 
-   local e
-   for i = 1, self.entities.size do
-      e = self.entities:get(i)
-
-      self:checkEntity(e)
-   end
-
    return self
 end
 
@@ -242,8 +215,6 @@ function World:emit(eventName, ...)
       error("bad argument #1 to 'World:emit' (String expected, got "..type(eventName)..")")
    end
 
-   self:flush()
-
    local listeners = self.events[eventName]
 
    if listeners then