The Communist League was an international political party established in June 1847 in London, England. The organization was formed through the merger of the League of the Just, headed by Karl Schapper and the Communist Correspondence Committee of Brussels, Belgium, in which Karl Marx and Friedrich Engels were the dominant personalities. The Communist League is regarded as the first Marxist political party and it was on behalf of this group that Marx and Engels wrote the Communist Manifesto late in 1847. The Communist League was formally disbanded in 1852, following the Cologne Communist Trial.

During the decade of the 1840s the word "communist" came into general use to describe those who hailed the left wing of the Jacobin Club of the French Revolution as their ideological forefathers. This political tendency saw itself as egalitarian heritors of the 1795 Conspiracy of Equals headed by Gracchus Babeuf. The sans-culottes of Paris which had decades earlier been the base of support for Babeuf — artisans, journeymen, and the urban unemployed — was seen as a potential foundation for a new social system based upon the modern machine production of the day.