diff --git a/concord/component.lua b/concord/component.lua
index 7e0ae2d..7a81a52 100644
--- a/concord/component.lua
+++ b/concord/component.lua
@@ -8,6 +8,8 @@ function Component.new(populate)
    local component = setmetatable({
       __populate = populate,
       __inherit  = inherit,
+
+      __isComponent = true,
    }, Component)
 
    component.__mt = {__index = component}
diff --git a/concord/entity.lua b/concord/entity.lua
index 4f2c022..f251002 100644
--- a/concord/entity.lua
+++ b/concord/entity.lua
@@ -1,5 +1,6 @@
 local PATH = (...):gsub('%.[^%.]+$', '')
 
+local Type = require(PATH..".type")
 local List = require(PATH..".list")
 
 local Entity = {}
@@ -12,6 +13,8 @@ function Entity.new()
       components = {},
       removed    = {},
       instances  = List(),
+
+      __isEntity = true,
    }, Entity)
 
    return e
@@ -22,6 +25,10 @@ end
 -- @param ... The values passed to the Component
 -- @return self
 function Entity:give(component, ...)
+   if not Type.isComponent(component) then
+      error("bad argument #1 to 'Entity:give' (Component expected, got "..type(component)..")", 2)
+   end
+
    self.components[component] = component:__initialize(...)
 
    return self
@@ -31,6 +38,10 @@ end
 -- @param component The Component to remove
 -- @return self
 function Entity:remove(component)
+   if not Type.isComponent(component) then
+      error("bad argument #1 to 'Entity:remove' (Component expected, got "..type(component)..")")
+   end
+
    self.removed[component] = true
 
    return self
@@ -65,6 +76,10 @@ end
 -- @param component The Component to get
 -- @return The Bag from the Component
 function Entity:get(component)
+   if not Type.isComponent(component) then
+      error("bad argument #1 to 'Entity:get' (Component expected, got "..type(component)..")")
+   end
+
    return self.components[component]
 end
 
@@ -72,6 +87,10 @@ end
 -- @params component The Component to check against
 -- @return True if the entity has the Bag. False otherwise
 function Entity:has(component)
+   if not Type.isComponent(component) then
+      error("bad argument #1 to 'Entity:has' (Component expected, got "..type(component)..")")
+   end
+
    return self.components[component] ~= nil
 end
 
diff --git a/concord/init.lua b/concord/init.lua
index fe40f14..8770362 100644
--- a/concord/init.lua
+++ b/concord/init.lua
@@ -1,5 +1,7 @@
 local PATH = (...):gsub('%.init$', '')
 
+local Type = require(PATH..".type")
+
 local Concord = {}
 
 --- Initializes the library with some optional settings
@@ -17,10 +19,18 @@ function Concord.init(settings)
       Concord.instances = {}
 
       Concord.addInstance = function(instance)
+         if not Type.isInstance(instance) then
+            error("bad argument #1 to 'Concord.addInstance' (Instance expected, got "..type(instance)..")", 2)
+         end
+
          table.insert(Concord.instances, instance)
       end
 
       Concord.removeInstance = function(instance)
+         if not Type.isInstance(instance) then
+            error("bad argument #1 to 'Concord.addInstance' (Instance expected, got "..type(instance)..")", 2)
+         end
+
          for i, instance in ipairs(Concord.instances) do
             table.remove(Concord.instances, i)
             break
diff --git a/concord/instance.lua b/concord/instance.lua
index 3247c09..b4a75f2 100644
--- a/concord/instance.lua
+++ b/concord/instance.lua
@@ -1,6 +1,9 @@
 local PATH = (...):gsub('%.[^%.]+$', '')
 
-local List = require(PATH..".list")
+local Entity = require(PATH..".entity")
+local System = require(PATH..".system")
+local Type   = require(PATH..".type")
+local List   = require(PATH..".list")
 
 local Instance = {}
 Instance.__index = Instance
@@ -13,6 +16,8 @@ function Instance.new()
       systems      = List(),
       events       = {},
       removed      = {},
+
+      __isInstance = true,
    }, Instance)
 
    return instance
@@ -22,6 +27,10 @@ end
 -- @param e The Entity to add
 -- @return self
 function Instance:addEntity(e)
+   if not Type.isEntity(e) then
+      error("bad argument #1 to 'Instance:addEntity' (Entity expected, got "..type(e)..")", 2)
+   end
+
    e.instances:add(self)
    self.entities:add(e)
    self:checkEntity(e)
@@ -33,6 +42,10 @@ end
 -- @param e The Entity to check
 -- @return self
 function Instance:checkEntity(e)
+   if not Type.isEntity(e) then
+      error("bad argument #1 to 'Instance:checkEntity' (Entity expected, got "..type(e)..")", 2)
+   end
+
    for i = 1, self.systems.size do
       self.systems:get(i):__check(e)
    end
@@ -44,6 +57,10 @@ end
 -- @param e The Entity to mark
 -- @return self
 function Instance:removeEntity(e)
+   if not Type.isEntity(e) then
+      error("bad argument #1 to 'Instance:removeEntity' (Entity expected, got "..type(e)..")", 2)
+   end
+
    self.removed[#self.removed + 1] = e
 
    return self
@@ -77,6 +94,10 @@ end
 -- @param enabled If the system is enabled. Defaults to true
 -- @return self
 function Instance:addSystem(system, eventName, callback, enabled)
+   if not Type.isSystem(system) then
+      error("bad argument #1 to 'Instance:addSystem' (System expected, got "..type(system)..")", 2)
+   end
+
    if system.__instance and system.__instance ~= self then
       error("System already in instance '" ..tostring(system.__instance).."'")
    end
@@ -106,6 +127,10 @@ end
 -- @param callback The callback it was registered with. Defaults to eventName
 -- @return self
 function Instance:enableSystem(system, eventName, callback)
+   if not Type.isSystem(system) then
+      error("bad argument #1 to 'Instance:enableSystem' (System expected, got "..type(system)..")", 2)
+   end
+
    return self:setSystem(system, eventName, callback, true)
 end
 
@@ -115,6 +140,10 @@ end
 -- @param callback The callback it was registered with. Defaults to eventName
 -- @return self
 function Instance:disableSystem(system, eventName, callback)
+   if not Type.isSystem(system) then
+      error("bad argument #1 to 'Instance:disableSystem' (System expected, got "..type(system)..")", 2)
+   end
+
    return self:setSystem(system, eventName, callback, false)
 end
 
@@ -125,17 +154,23 @@ end
 -- @param enable The state to set it to
 -- @return self
 function Instance:setSystem(system, eventName, callback, enable)
+   if not Type.isSystem(system) then
+      error("bad argument #1 to 'Instance:setSystem' (System expected, got "..type(system)..")", 2)
+   end
+
    callback = callback or eventName
 
-   local listeners = self.events[eventName]
+   if callback then
+      local listeners = self.events[eventName]
 
-   if listeners then
-      for i = 1, #listeners do
-         local listener = listeners[i]
+      if listeners then
+         for i = 1, #listeners do
+            local listener = listeners[i]
 
-         if listener.system == system and listener.callback == callback then
-            listener.enabled = enable
-            break
+            if listener.system == system and listener.callback == callback then
+               listener.enabled = enable
+               break
+            end
          end
       end
    end
@@ -148,6 +183,10 @@ end
 -- @param ... Parameters passed to listeners
 -- @return self
 function Instance:emit(eventName, ...)
+   if not eventName or type(eventName) ~= "string" then
+      error("bad argument #1 to 'Instance:emit' (String expected, got "..type(eventName)..")")
+   end
+
    self:flush()
    
    local listeners = self.events[eventName]
diff --git a/concord/pool.lua b/concord/pool.lua
index 3fcf4c1..0faa85f 100644
--- a/concord/pool.lua
+++ b/concord/pool.lua
@@ -15,6 +15,8 @@ function Pool.new(name, filter)
    pool.name   = name
    pool.filter = filter
 
+   pool.__isPool = true
+
    return pool
 end
 
diff --git a/concord/system.lua b/concord/system.lua
index ffe3e47..36fbd94 100644
--- a/concord/system.lua
+++ b/concord/system.lua
@@ -11,6 +11,8 @@ System.mt    = {
          __all      = {},
          __pools    = {},
          __instance = nil,
+
+         __isSystem = true,
       }, systemProto)
 
       for _, filter in pairs(systemProto.__filter) do
diff --git a/concord/type.lua b/concord/type.lua
new file mode 100644
index 0000000..204aa79
--- /dev/null
+++ b/concord/type.lua
@@ -0,0 +1,19 @@
+local Type = {}
+
+function Type.isComponent(t)
+   return type(t) == "table" and t.__isComponent
+end
+
+function Type.isEntity(t)
+   return type(t) == "table" and t.__isEntity
+end
+
+function Type.isSystem(t)
+   return type(t) == "table" and t.__isSystem
+end
+
+function Type.isInstance(t)
+   return type(t) == "table" and t.__isInstance
+end
+
+return Type
\ No newline at end of file