The Atari ST is a line of personal computers from Atari Corporation and the successor to the Atari 8-bit family. The initial model, the 520ST, saw limited release in April–June 1985 and was widely available in July. It was the first personal computer with a bitmapped color GUI, using a version of Digital Research's GEM from February 1985.

The 1040ST, released in 1986 with 1 MB of RAM, was the first home computer with a cost-per-kilobyte of less than US$1. It is part of a mid-1980s generation of computers with 16- or 32-bit processors, 256 KB or more of RAM, and mouse-controlled graphical user interfaces. (Other examples include the Macintosh, Amiga, Apple IIGS, and Acorn Archimedes.)

"ST" officially stands for "Sixteen/Thirty-two", referring to the Motorola 68000's 16-bit external bus and 32-bit internals. The system was designed by a small team led by Shiraz Shivji.

The ST was sold with either Atari's color monitor or less expensive monochrome monitor. Color graphics modes were available only on the former while the highest-resolution mode required the monochrome monitor. Some later models could display the color modes on a TV.

In some markets, particularly Germany, the ST gained a foothold for CAD and desktop publishing. With its built-in MIDI ports, it was popular for music sequencing and as a controller of musical instruments among amateurs and professional musicians.

It was superseded by the Atari STE, Atari TT, Atari MEGA STE and Falcon computers.