Studied at Saint St. Petersburg University.
1892 first arrested in Saint St. Petersburg for membership of a circle engaged in revol work among student youth and for distributing illegal literature After his release from prison worked for illegal “Red Cross” group and for Saint St. Petersburg Liberation of Labor Group. 1893 exiled to Vilnius, where he was active in Jewish workers’ movement.
1895 returned to Saint St. Petersburg and joined Lenin’s group of “Old Revolutionaries”. 1896 arrested and 1897 exiled for three years to Turukhansk. After his exile helped prepare and edit “Iskra”.
At 2nd Russian Social-Democratic Workers’ Party Congress headed minority faction. October 1905-1907 lived in Russia and led Russian Social-Democratic Workers’ Party (Menshevik) faction. Attended London Party Congress.
Remained abroad and helped edit Menshevik paper “Golos sotsial-demokratov”. Took moderate liquidationist stand. Adopted centrist stand as regards the war.
Attended Zimmerwald and Kienthal Party Conferences. After 1917 February Revol returned to Russia and sided with Menshevik internationalists. Opposed 1917 October Revol.
1920 member, Moscow Soviet. Until 1920 lived in Russian Soviet Federative Socialist Republic and led Russian Social-Democratic Workers’ Party Mensheviks. 1921 exiled from Russian Soviet Federative Socialist Republic and edited Russian Social-Democratic Workers’ Party journal “Sotsialisticheskiy vestnik”.