The International Institute of Social History (IISH/IISG) is one of the largest archives of labor and social history in the world. Located in Amsterdam, its one million volumes and 2,300 archival collections include the papers of major figures and institutions in radical leftist thought. The IISH was founded in 1935 by Nicolaas Posthumus as an independent scientific institute. It is part of the Royal Netherlands Academy of Arts and Sciences.