Seventy five years ago the Partido Obrero de Unificación Marxista (Workers’ Party of Marxist Unification) was formed in Barcelona. The POUM was to play a central role in the revolution that unfolded as a result of the military uprising of July 1936. This contribution looks at the context of the party’s founding, the development of the two organisations that formed it and its ideological basis. In particular, it examines its attempts to extend the process of unification to include other Marxists. These moves towards unity contrasted with the growing campaign against the new party by the Communists; a campaign that would prove to be the first step towards the repression of the party during the Civil War accused of Trotskyism and by extension ...