Yedinstvo or Edinstvo (Russian: Единство, meaning Unity) was a faction within the Russian Social Democratic Labor Party (RSDLP) between 1914 and 1917 and then a small independent party in 1917 and 1918. It was led by Georgi Plekhanov.
Plekhanov was a prominent Russian Marxist theoretician and journalist who lived in exile in Europe from the early 1880s until 1917. Although he was revered by Russian social democrats as the founding father of Russian Marxism, post-1900 he was gradually eclipsed within the RSDLP by younger leaders like Julius Martov, Vladimir Lenin, Alexander Bogdanov, and others. In the immediate aftermath of the split between Lenin's Bolsheviks and Martov's Mensheviks in August 1903, Plekhanov first sided with Lenin, but in late 1903 he went over to the Mensheviks. When the Bolsheviks and the Mensheviks further split in the wake of the Russian Revolution of 1905, Plekhanov formed a small faction within the Mensheviks known as "Party Mensheviks" (sometimes translated as "Pro-party Mensheviks"). He was critical of both the Bolsheviks and of most Mensheviks, whom he saw as concentrating on legal oppositionist work in Russia at the expense of revolutionary activities, using his newspaper, Dnevnik sotsialdemokrata (Diary of a Social Democrat), as bully pulpit.
In 1912 the RSDLP formally split into Lenin's supporters on the one hand and a coalition of Mensheviks, Leon Trotsky's supporters and ethnic social democratic groups on the other hand. Plekhanov and some other social democrats refused to join either side. With the split becoming deeper in 1913 (e.g. the social democratic faction in the State Duma split in September 1913), those who didn't join either side began forming their own organizations, e.g. the Mezhraiontsy group was formed in November 1913. In early 1914, Plekhanov followed suit and formed his own group, Yedinstvo (Unity), with his old friends and followers Vera Zasulich and Leo Deutsch The group was founded abroad, but its supporters became active in Russia proper as early as the spring of 1914 and published 4 issues of the newspaper Yedinstvo in St. Petersburg in May and June 1914.