Leopold Haimson, Professor Emeritus of Russian History, was a longtime faculty member of the Harriman Institute, and beloved teacher, colleague and friend. In his famously demanding seminars, he mentored several generations of graduate students, many of whom went on to distinguished careers. Haimson’s influential first book, The Russian Marxists and the Origins of Bolshevism (1955), was notable for its artful weaving of intellectual history and psychologically acute biographies of leading revolutionaries. In 1964 he initiated a catalytic debate with the publication in Slavic Review of a two-part article on the viability of late imperial Russia on the eve of the First World War and the inevitability of revolution. In the 1970s and 1980s he took a more comparative approach to the study of pre-revolutionary and revolutionary Russia, working with the sociologist Charles Tilly and the economic historian Giulio Sapelli on strike waves and revolutions in an international perspective. He continued to publish widely on the social and political history of Russia before and during 1917. During the Soviet era, Haimson worked hard to set up collaborations with Soviet colleagues, and he developed close ties with the Maison des Sciences de l’Homme in Paris. Throughout his career he showed a deep interest in questions of individual and collective identities, drawing on cultural anthropology to explore Russian political culture and on psychology to analyze the actions of key individuals in the period he studied in such a rich and productive way.