Amadeo Bordiga (13 June 1889 – 23 July 1970) was an Italian Marxist, a contributor to communist theory, the founder of the Communist Party of Italy (PCd'I), a leader of the Communist International (Comintern) and later a leading figure of the International Communist Party.
Bordiga was originally associated with the PCd'I, but he was expelled in 1930 after being accused of Trotskyism.
Later on following World War II, Bordiga moved more explicitly towards a left communist position and was one of the more notable Western European representatives of this tendency.