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 Atari 520ST, had 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 Atari 1040ST, released in 1986 with 1 MB of RAM, was the first home computer with a cost-per-kilobyte of less than US$1.

"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. Alongside the Macintosh, Amiga, Apple IIGS, and Acorn Archimedes, the ST 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.

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It was superseded by the Atari STE, Atari TT, Atari MEGA STE and Falcon computers.

<computer> A personal computer released by Atari in 1985. The "ST" stands for "Sixteen/Thirty-two", from the {Motorola 68000}'s 16-bit external bus and 32-bit processor. The original 520ST model had an external floppy drive and power supply whereas the 1040ST had them built-in. The 520 and later 520STFM came with 512 KB of RAM, the 1040 had 1 MB. Several upgraded models followed, up to the 1993 {Motorola 68030} based Falcon. The ST was the first home computer with built-in MIDI ports and plenty of MIDI software. A wide range of other software from office to games was also available. (2006-10-30)

Atari ST User was a British computer magazine aimed at users of the Atari ST range. It started life as a pull-out section in Atari User magazine.