Joaquín Maurín Juliá (or Joaquim Maurín in Catalan; 12 January 1896—5 November 1973) was a Spanish Communist politician and revolutionary, leader of the Workers and Peasants Bloc (BOC) and of the Workers' Party of Marxist Unification (POUM). He was active mainly in Catalonia.
Born in Bonansa, Huesca (Aragon), Maurín engaged in revolutionary politics from early youth, standing trial on several occasions. After law studies, he practiced in Lleida (Catalonia), where he became affiliated with the Anarchist trade union Confederación Nacional del Trabajo (CNT). In 1920, Joaquín Maurín was elected local secretary for the CNT, as well as the editor of its weekly Lucha Social. In 1921, he represented the movement at the Profintern Congress in Moscow, the capital of Bolshevist Russia. Upon his return, he was elected general secretary of the CNT, shortly before being arrested and detained (February 1922). After his release, Joaquín Maurín founded the Comités Sindicalistas Revolucionarios ("Revolutionary Trade Union Committees") as a Bolshevik group within the CNT. He also gave the Committees their own press tribune, La Batalla (in December).
In 1924, he led his La Batalla into a merger with the Communist Party of Spain, taking charge of organizing the latter's local wing, the Catalan-Balearic Communist Federation (FCCB). During the crackdown on opposition parties ordered by dictator Miguel Primo de Rivera, Maurín was arrested and jailed (January 1925). He was released in 1927, opting to leave Spain for Paris. However, he returned to Barcelona in 1930, and worked for the reanimation of La Batalla in the months before the proclamation of the Second Spanish Republic (early 1931). He became opposed to Stalinist policies in the Soviet Union, taking a stand which saw him grouped with the emergent international Right Opposition. He split with the Spanish Communist Party, leading the FCCB into independent politics (the wing’s place in the Stalinist body was quickly taken over by the Communist Party of Catalonia).