While every archive is unique by definition, the German archival collections at the IISH are truly exceptional. During the Institute's early years, the acquisition of the papers of the labour movement's founding fathers Karl Marx, Friedrich Engels, and Moses Hess laid the basis for its collections. These papers were part of the historical archives of the German Social Democratic Party (SPD), purchased in 1938 after a stiff competition between the Moscow Marx-Engels Institute and the IISH. In addition to these impressive names, the collection also includes many others, such as the theorists Karl Kautsky and Eduard Bernstein who each contributed in his own way to the Marxism of the Second International.
The IISH and the legal successor of the Marx-Engels Institute in Moscow (RGASPI) established an amicable relationship in the early 1990s. As a consequence, microfilm copies from the holdings in Moscow came to Amsterdam. These include the papers of Clara Zetkin and many important accessions to the archives mentioned in this section. The records of Sozialistische Monatshefte (Joseph Bloch), seized by the Nazis and then the Soviet Red Army during World War II, were officially returned to their original owner, the IISH, in 2002.
"Western Marxism", which functioned independently of and often in opposition to both communism and social democracy during the interwar period, appears in the collections of Karl Korsch, Otto Rühle and Paul Mattick at the IISH. Mattick lived long enough to personify the link between the older Marxist tradition and the Marxist renaissance in Western Europe and the United States during the 1970s.
The archives of Rosa Luxemburg and Karl Liebknecht are exquisite but not extensive. The greater part of the Karl Liebknecht papers was deposited in Moscow and can now be consulted in microform at the IISH.
The course of life of German social democracy is very well represented in the archival collections at the IISH. Highlights include the social-democratic movement's role as opposition within the Empire until 1914. The opposition figures in the papers of August Bebel, Wilhelm Liebknecht, Julius Motteler, and Georg von Vollmar. Wilhelm Dittman's papers relate the split that occurred in the movement during World War I. The papers of Otto Braun, Wolfgang Heine, and Albert Grzesinski reflect the movement's major role in the Weimar period.
The social-democratic movement's part in the resistance during World War II and the emigration is well documented in the Neu Beginnen and Paul Hertz collections. After 1945, the SPD became the target of opposition both within and outside the party. The papers of Wolfgang Abendroth and Willy Huhn reflect this situation. In addition, an extra-parliamentary protest affected the political establishment. The Konrad Böhmer and Kommune I collections consider this aspect.
Prominent in the anarchist collections at the IISH are the archives of Gustav Landauer, Max Nettlau and Rudolf Rocker. Rudolf Rocker co-founded both the Freie Arbeiter-Union Deutschlands in 1919 and the syndicalist International Working Men's Association in 1922. The extensive correspondence in the papers of Helmut Rüdiger sheds more light on these syndicalist organizations, as Rüdiger worked for both.