International Institute of Social History

The International Institute of Social History (Dutch: "Internationaal Instituut voor Sociale Geschiedenis"; abbreviation: "IISG") is a historical research institute in Amsterdam. It was founded in 1935 by Nicolaas Posthumus. It has collections of the most works and manuscripts by socialist including Karl Marx, Friedrich Engels and Rosa Luxemburg. It is now part of the Royal Netherlands Academy of Arts and Sciences.