This book explores the confrontation of radically assimilated Jews with the violent collapse of their envisioned integration into a cosmopolitan European society, which culminated during the Holocaust. This confrontation is examined through the biography of the German-speaking intellectual and prominent communist theoretician of the Jewish question Otto Heller (1897-1945), focusing on the tension between his Jewish origins and his universalistic political convictions. Radical Assimilation in the Face of the Holocaust traces the development of Hellerʼs position on the Jewish question in three phases: how he grew up to become a typical Central European "non-Jewish Jew" (1897-1931); how he became exceptional in that category by focusing his intellectual work on the Jewish question (1931-1939); and how he reacted to the persecution and murder of European Jewry as a member of the Resistance in occupied France and in Auschwitz (1939-1945). Breaking with the common portrayal of Heller as a self-hating Jew, Tom Navon argues instead that Heller came to lay the foundations for the groundbreaking recognition by communists of worldwide Jewish national solidarity.