diff --git a/lib/instance.lua b/lib/instance.lua
index e3f4656..451ef50 100644
--- a/lib/instance.lua
+++ b/lib/instance.lua
@@ -107,6 +107,8 @@ function Instance:addSystem(system, eventName, callback, enabled)
    if not self.systems:has(system) then
       self.systems:add(system)
       system.__instance = self
+
+      system:addedTo(self)
    end
 
    if eventName then
@@ -177,7 +179,14 @@ function Instance:setSystem(system, eventName, callback, enable)
             local listener = listeners[i]
 
             if listener.system == system and listener.callback == callback then
+               if enable and not listener.enabled then
+                  system:enabledCallback(callback)
+               elseif not enable and listener.enabled then
+                  system:disabledCallback(callback)
+               end
+
                listener.enabled = enable
+
                break
             end
          end
diff --git a/lib/system.lua b/lib/system.lua
index 0027332..04cf6a4 100644
--- a/lib/system.lua
+++ b/lib/system.lua
@@ -42,11 +42,6 @@ function System.new(...)
    return systemProto
 end
 
---- Default initialization function.
--- @param ... Varags
-function System:init(...)
-end
-
 --- Builds a Pool for the System.
 -- @param baseFilter The 'raw' Filter
 -- @return A new Pool
@@ -140,6 +135,11 @@ function System:__has(e)
    return self.__all[e] and true
 end
 
+--- Default callback for system initialization.
+-- @param ... Varags
+function System:init(...)
+end
+
 --- Default callback for adding an Entity.
 -- @param e The Entity that was added
 function System:entityAdded(e)
@@ -162,6 +162,21 @@ end
 function System:entityRemovedFrom(e, pool)
 end
 
+-- Default callback for when the System is added to an Instance.
+-- @param instance The Instance the System was added to
+function System:addedTo(instance)
+end
+
+-- Default callback for when a System's callback is enabled.
+-- @param callbackName The name of the callback that was enabled 
+function System:enabledCallback(callbackName)
+end
+
+-- Default callback for when a System's callback is disabled.
+-- @param callbackName The name of the callback that was disabled 
+function System:disabledCallback(callbackName)
+end
+
 return setmetatable(System, {
    __call = function(_, ...) return System.new(...) end,
 })