This collection of papers thoroughly documents most aspects of the life and work of Boris Sapir, particularly his activities as a Menshevik leader and writer in the Russian emigration, and as an historian of Russian populism and socialism. Materials on his work as a Menshevik include correspondence with his colleagues, significant files on the "Foreign Delegation" in Germany in the 1920s-30s, and on its "New York Center" in the 1940s-50s, an extensive collection of photographs of his fellow Mensheviks, and files and manuscripts relating to the Inter-University Project on the History of Menshevism from the 1960's. Concerning Sapir's career as an historian and archivist, there is material he used for his many publications in the field, correspondence with scholars and students (mostly asking his guidance, or thanking him for it), and some of his own manuscripts. There is a great deal of material on his personal life as well, in particular in his correspondence, in files on his biography, bibliography, and posthumous "rehabilitation, " and in his manuscript and photograph collections. Less well documented are his two decades of work with the American Jewish Joint Distribution Committee. Besides the importance of the papers generated by Sapir himself, this collection is an excellent source for work on the Mensheviks because he was entrusted by his friends and colleagues with their own papers. These materials help to document the history of Menshevism particularly from the still hopeful years of the "Foreign Delegation" in Germany in the 1920s, to the last years of the "New York Center, " including its internal disputes in the 1950s, soon followed by the deaths of those Mensheviks who had survived the many years of wars and persecutions. Some of the materials go back to the pre-revolutionary era, through memoirs on the early years of Russian Marxism (1890s-1917). The entire collection consists of approximately 24, 000 items, spanning 1898-1992. Most of it consists of Sapir's own papers.