The Sinclair ZX80 is a home computer brought to market in 1980 by Science of Cambridge Ltd. (later to be better known as Sinclair Research). It is notable for being the first computer (unless you consider the MK14) available in the United Kingdom for less than a hundred pounds (£99.95). It was available in kit form, where purchasers had to assemble and solder it together, and as a ready-built version at a slightly higher cost for those without the skill or inclination to build their own unit. The ZX80 was very popular straight away, and for some time there was a waiting list of several months for either version of the machine.

The ZX80 was named after the Z80 processor with the 'X' for "the mystery ingredient".

Internally, the machine was designed by Jim Westwood around a Z80 central processing unit with a clock speed of 3.25 MHz, and was equipped with 1 kB of static RAM and 4 kB of read-only memory (ROM). The ZX80 was designed around readily available TTL chips; the only proprietary technology was the firmware. While the successor ZX81 used a semi-custom chip (a ULA or Uncommitted Logic Array), this merely combined the functions of the earlier hardware onto a single chip — the hardware and system programs (except the BASIC versions) were very similar, with the only significant difference being the NMI-generator necessary for slow mode in the ZX81. (See ZX81 for technical details.) Both computers can be made by hobbyists using commercially available discrete logic chips or FPGAs.

Sir Clive Marles Sinclair (born 30 July 1940) is an English entrepreneur and inventor, most commonly known for his work in consumer electronics in the late 1970s and early 1980s.

After spending several years as assistant editor of Practical Wireless and Instrument Practice, Sinclair founded Sinclair Radionics in 1961, where he produced the first slim-line electronic pocket calculator in 1972 (the Sinclair Executive). Sinclair later moved into the production of home computers and produced the Sinclair ZX80, the UK's first mass-market home computer for less than GB£100, and later, with Sinclair Research, the ZX81 and ZX Spectrum; the latter is widely recognised for its importance in the early days of the British home computer industry. Sinclair stated in 2010 that he does not use computers himself, using the telephone in preference to email.

Knighted in 1983, Sinclair formed Sinclair Vehicles and released the Sinclair C5, a battery electric vehicle that was a commercial failure. Since then Sinclair has concentrated on personal transport, including the A-bike, a folding bicycle for commuters that weighs 5.5 kilograms (12 lb) and folds down small enough to be carried on public transport.