System 3, System/3 or System III may refer to:
Computing and electronics Acorn System 3, a home computer produced by Acorn Computers from 1980 Cromemco System Three, a home computer produced by Cromemco from 1978 IBM System/3, a low-end business computer manufactured between 1969 and 1985 IBM System/3X, a line of general business midrange computers manufactured from 1975 Operating System/3, operating system made by UNIVAC System Software 3, operating system made by Apple System 3 (software company), a software development firm UNIX System III, operating system released by AT&T Zenith System 3, a line of television models by Zenith Electronics
Other System 3 in Trilogy, album by Criss Angel and Klay Scott System 3 FC, a football club in St Vincent and the Grenadines STS-3 (Space Transportation System-3), the Space Shuttle mission
See also Series 3 (disambiguation)