Tiny BASIC is a family of dialects of the BASIC programming language that can fit into 4 or fewer KBs of memory. Tiny BASIC was designed in response to the open letter published by Bill Gates complaining about users pirating Altair BASIC, which sold for $150. Tiny BASIC was intended to be a completely free version of BASIC that would run on the same early microcomputers.

Tiny BASIC was released as a specification, not an implementation, published in the September 1975 issue of the People's Computer Company (PCC) newsletter. The article invited programmers to implement it on their machines and send the resulting assembler language implementation back for inclusion in a series of three planned newsletters. Li-Chen Wang, author of Palo Alto Tiny BASIC, coined the term "copyleft" to describe this concept. The community response was so overwhelming that the newsletter was relaunched as Dr. Dobb's Journal, the first regular periodical to focus on microcomputer software. Dr. Dobb's lasted in print form for 34 years and then online until 2014, when its website became a static archive.

The small size and free source code made these implementations invaluable in the early days of microcomputers in the mid-1970s, when RAM was expensive and typical memory size was only 4 to 8 KB. While the minimal version of Microsoft's Altair BASIC would also run in 4 KB machines, it left only 790 bytes free for BASIC programs. More free space was a significant advantage of Tiny BASIC. To meet these strict size limits, Tiny BASIC dialects generally lacked a variety of features commonly found in other dialects, for instance, most versions lacked string variables, lacked floating-point math, and allowed only single-letter variable names.

Tiny BASIC implementations are still used today, for programming microcontrollers such as the Arduino.