Marxist revolutionary party ancestral to the Communist Party of the Soviet Union. Founded in 1898 in Minsk, the Social-Democratic Party held that Russia could achieve socialism only after developing a bourgeois society with an urban proletariat. It rejected the populist idea that the peasant commune, or mir, could be the basis of a socialist society that could bypass the capitalist stage.

Most of the leaders elected at the founding congress were soon arrested. The second congress, in Brussels and London in July–August 1903, was dominated by the argument between the Bolshevik wing of the party, led by Vladimir Lenin, and the Menshevik wing, led by L. Martov, over Lenin's proposals for a party composed of disciplined professional revolutionaries. Georgy Plekhanov, one of the founders of Russian Marxism, took a generally middle position. This argument dominated the internal life of the party. Party members played a major role in the unsuccessful Russian Revolution of 1905, in which one Social-Democratic leader, Leon Trotsky, was elected president of the St. Petersburg Soviet. In the turmoil of 1917 the Bolsheviks broke definitively with their Menshevik rivals and, after the Bolshevik Revolution in 1917, changed their name to the Russian Communist Party (Bolshevik). Their rivals, the Mensheviks, were finally suppressed after the end of the Russian Civil War.