This chapter overviews some of the Windows technologies that provides some background to understanding the Microsoft middleware technologies. The world of Middleware has seen several different Microsoft offerings. Back in the 1990s, Distributed Component Object Model (DCOM) was a major competitor to Common Object Request Broker Architecture (CORBA). Starting in 2002,.NET Remoting became a widely used Microsoft middleware. Then in 2006, Microsoft released Windows Communication Foundation, which has been a competitor to JAX-WS, JAX-RS, and AJAX, while.NET Remoting has been a Microsoft competitor to CORBA and to Enterprise Java Beans. Dynamic Link Library (DLL) files are what Microsoft used to implement a shared library. A shared library contains library routines that are stored separately from the calling program executable files. The Microsoft Common Language Runtime (CLR) is the virtual machine used by all.NET routines. CLR implements a program code execution environment which is defined by the Common Language Infrastructure (CLI).