Amadeo Bordiga (13 June 1889 – 25 July 1970) was an Italian Marxist theorist, revolutionary socialist, founder of the Communist Party of Italy (PCI), member of the Communist International (Comintern) and later a leading figure of the International Communist Party. Bordiga was originally associated with the PCI, but he was expelled in 1930 after being accused of Trotskyism.
Bordiga is viewed as one of the most notable representatives of Left communism in Europe.
Bordiga was born at Resina in the province of Naples in 1889. His father, Oreste Bordiga, was an esteemed scholar of agricultural science, whose authority was especially recognized in regard to the centuries-old agricultural problems of Southern Italy. His mother, Zaira degli Amadei, was descended from an ancient Florentine family and his maternal grandfather Count Michele Amadei was a conspirator in the struggles of the Risorgimento. His paternal uncle, Giovanni Bordiga, another militant of the Risorgimento, was a mathematician and professor at the University of Padua. Bordiga's upbringing, while being thoroughly radical, was also of a highly scientific nature.
An opponent of the Italian colonial war in Libya, Bordiga was introduced to the Italian Socialist Party (PSI) by his high-school physics teacher in 1910. Bordiga eventually founded the Karl Marx Circle in 1912, where he would meet his first wife, Ortensia De Meo.
Bordiga graduated with a degree in engineering from University of Naples Federico II in 1912.
Bordiga married Ortensia De Meo in 1914. They had two children, Alma and Oreste. Ortensia died in 1955, and Bordiga married Ortensia's sister, Antonietta De Meo ten years later in 1965.
Within the newly founded Karl Marx Circle, Bordiga rejected a pedagogical approach to political work and developed a "theory of the Party", whereby the organization was meant to display non-immediate goals as a rally of similarly minded people and not necessarily a body of the working class.