Joined the revolutionary movement, 1887. Active in Odessa and Petersburg. Menshevik, 1903-1917.
Lecturer at the Social Democratic Party school at Longjumeau, 1911. First editor of the collected works of Marx and Engels (in the original German), 2 vols, published in Germany before 1916. After the October Revolution 1917, joined the Bolsheviks (for a short time leaving the party after Brest-Litovsk).
Founder and director of the Marx-Engels Institute (the chief ideological institution of Marxism) in Moscow, 1921-1931. Edited the collected works of Marx, Engels, Plekhanov, Hegel. Uncharacteristically for Bolshevik Party members, tried courageously to protect his employees from arrest during the Stalinist purges.
Expelled from the party in 1931, dismissed, exiled (at first to Leningrad, later to Saratov). Arrested in 1937, and died in prison.