Formed in 1898 in Minsk. At the first congress, the Tsarist Security arrested all its members.

Banded together in opposition to the Narodniki revolutionaries, the Social-Democrats (SDs) programme was to unite and organise the peasantry and proletariat towards Socialist revolution. The SDs regarded the proletariat as the only wholly revolutionary class in Russia, while some of the peasantry, the serfs, were considered revolutionary, while the wealthy peasants (the kulaks) were seen as reactionary.

In 1903 the Second Congress of the party met in Belgium and England. After the congress the party split into the Bolsheviks (majority party) and Mensheviks (minority party).