Left communism is the range of communist viewpoints held by the communist left, which criticizes the political ideas of the Bolsheviks at certain periods, from a position that is asserted to be more authentically Marxist and proletarian than the views of Leninism held by the Communist International after its first and during its second congress.

Left Communists see themselves to the left of Leninists (whom they tend to see as 'left of capital', not socialists), anarchist communists (some of whom they consider internationalist socialists) as well as some other revolutionary socialist tendencies (for example De Leonists, who they tend to see as being internationalist socialists only in limited instances).

Although she died before left communism became a distinct tendency, Rosa Luxemburg has heavily influenced most left communists, both politically and theoretically. Proponents of left communism have included Amadeo Bordiga, Herman Gorter, Anton Pannekoek, Otto Rühle, Sylvia Pankhurst and Paul Mattick.