A library of object-oriented routines that are used to develop an application and eliminate much of the tedium of programming today's graphical user interface-based applications. Classes are provided for a myriad of functions including multithreading, file I/O, memory arrays and windows and related GUI elements. Many of the base features of the class are used unchanged, while others are modified to suit the application.

Foundation classes cannot be used for every application. For example, the Windows version of this encyclopedia, which uses its own text display architecture, requires interfacing to Windows at a lower level than what foundation classes typically offer. Although even at a higher level than the standard API of the operating system, foundation classes still require programming ability and a reasonably high learning curve. They are not suited to end users as might be some kinds of application generators. See MFC, JFC, OWL and application generator.