Arnold Machin (30 September 1911 - 9 March 1999) was a British artist, sculptor, coin and stamp designer.
Born in Stoke-on-Trent in 1911, he started work at the age of 14 as an apprentice china painter at the Minton Pottery, then attended the Art Schools in Stoke-on-Trent and Derby, and the Royal Academy of Art in London. After spending the Second World War as a conscientious objector, he returned to modelling and sculpture, and created many notable ceramics which are now prized collectors' items. In 1946 he was elected an associate member of the Royal Academy, was appointed a Master of Sculpture from 1959 to 1966 and became the longest-serving member of the Academy. He was elected an Academician in 1956 and a Fellow of the Royal Society of British Sculptors. From 1951 he was a tutor at the Royal College of Art, where he enterd the culture that was to bring him his most celebrated commissions.

In 1964 Machin was chosen to design a new effigy of the Queen for the decimal coinage, which was to be introduced from 1968; this effigy was used for all British coins until 1984. In 1966 the Queen approved Machin's similar design for an effigy of her to be used on British definitive postage stamps; this was first used on the 4d value which was issued in March 1967, and has been used on all British definitive stamps (except more recent ones from Scotland, Wales, and Northern Ireland) ever since. It is thought that this design is the most reproduced work of art in history with, to date, approximately 150 billion examples produced.