Scope of ATL
The latest version of this topic can be found at Scope of ATL.
ATL allows you to easily create COM objects, Automation servers, and ActiveX controls. ATL provides built-in support for many of the fundamental COM interfaces.
ATL is shipped as source code which you include in your application. ATL also makes a DLL available (atl90.dll), which contains code that can be shared across components. However, this DLL is not necessary.