An operating system and object-oriented programming language that was developed at Xerox PARC. As an integrated environment, it eliminates the distinction between programming language and operating system. It also allows its user interface and behavior to be customized.

Smalltalk was the first object-oriented programming language to become popular. It was originally used to create prototypes of simpler programming languages and the graphical interfaces that are so popular today. Smalltalk was first run on Xerox's Alto computer, which was designed for it. In 1980, Smalltalk-80 was licensed to Tektronix, Apple, HP and TI for internal use. The first commercial release of Smalltalk was Methods from Digitalk in 1983, which later evolved into Visual Smalltalk. In 1997, Smalltalk became an ANSI standard (X3J20). See VisualWorks, Visual Smalltalk, VisualAge and Alto.