Microsoft BASIC is the foundation product of the Microsoft company. It first appeared in 1975 as Altair BASIC, which was the first BASIC (and indeed the first programming language) available for the MITS Altair 8800 hobbyist microcomputer.

The Altair BASIC interpreter was developed by Microsoft founders Paul Allen and Bill Gates with help from Monte Davidoff, using a self made Intel 8080 software simulator running on a minicomputer. It was delivered on paper tape and in its original version took 4 KB of memory. The extended 8K version was then generalized into BASIC-80 (8080/85, Z80), and ported into BASIC-68 (6800), BASIC-69 (6809), and MOS Technology 6502-BASIC (unfortunately spilling over to 9KB, in an era when 8K ROM chips were standard), as well as the 16-bit BASIC-86 (8086/88).

After the initial success of Altair BASIC, Microsoft BASIC became the basis for a lucrative software licensing business, being ported to the majority of the numerous home and personal computers of the 1970s and especially the 1980s, and extended along the way. Contrary to the original Altair BASIC, most home computer BASICs were resident in ROM, and thus were available on the machines at power-on in the form of the characteristic "READY."-prompt. Hence, Microsoft's and other variants of BASIC constituted a significant and visible part of many home computers' rudimentary operating systems.

Variants and derivatives of Microsoft BASIC

• Altair BASIC (MITS Altair and other S-100 computers)
• Amiga BASIC (Commodore Amiga family)
• Applesoft BASIC (Apple II family)
• Atari Microsoft BASIC I and II (Atari 8-bit family)
• BASICA ("BASIC Advanced") (PC-DOS, on IBM PC)
• Color BASIC (TRS-80 Color Computer, Dragon 32/64)
• Commodore BASIC (Commodore 8-bit family, incl C64)
• Extended Color BASIC (TRS-80 CoCo,  Dragon 32/64)
• IBM Cassette BASIC (PC-DOS, on original IBM PC)
• GW-BASIC (BASICA for MS-DOS, on PC compatibles)
• MBASIC (CP/M, on 8080/85 and Z80 based computers)
• MS BASIC for Macintosh (MacOS on Apple Macintosh)
• MSX BASIC (MSX standard home computers)
• QBasic (PC-DOS/MS-DOS on IBM PC and compatibles)
• Microsoft Level III BASIC (Tandy/Radio-Shack TRS-80)
• QuickBASIC (PC/MS-DOS on IBM PC and compatibles)
• TRS-80 Level II BASIC (Tandy/Radio-Shack TRS-80)
• Visual Basic (MS Windows on IBM PC and compatibles)
• WordBasic (pre-VBA) (ditto)