Ukrainian Social Democratic Labour Party

The Ukrainian Social Democratic Labour Party (Ukrainian: Украї́нська соціа́л-демократи́чна робітни́ча па́ртія, romanized: Ukrainska sotsial-demokratychna robitnycha partiia), also commonly known as Esdeky (Ukrainian: Есдеки, from the abbreviation USDRP, УСДРП), was a social-democratic political party active in the Russian Empire and later in the Ukrainian People's Republic. The party was formed in 1905 by members of the Revolutionary Ukrainian Party and followed the formula of Marxism introduced by the Erfurt Program of the Social Democratic Party of Germany. It also supported the ideas of national and cultural autonomy. The party was led by Volodymyr Vynnychenko, Symon Petliura, Mykola Porsh, Dmytro Antonovych, Lev Yurkevych, Mykhailo Tkachenko, and Mykola Kovalsky.

The party identified resolution of the national question as its priority and saw the struggle for social liberation of the working class as secondary. In the spring of 1905, in his polemics with Dmytro Antonovych, which were published in the party newspaper Pratsia, Mykola Porsh expressed the view, that social and economic oppression was conditioned by national subjugation. He insisted that the resolution of national issue was necessary in order to overcome social oppression.

In Soviet propaganda, the party was identified as a petty bourgeoisie nationalistic party, which named itself "Social Democratic" as a means of deception. Vladimir Lenin characterized the party's members as "representatives of the most low-grade, stupid and reactionary nationalism" who supposedly betrayed "not only interests of democracy in general, but also their own fatherland, Ukraine."