Left communism, or the communist left, describes a range of positions held by the left wing of communism, which criticises the political ideas and practices held by Marxist–Leninists and social democrats. Left communists assert positions which they regard as more authentically Marxist than the views of Marxism–Leninism espoused by the Communist International after its Bolshevization by Joseph Stalin and during its second congress. There have been two primary currents of left communism since World War I, namely the Italian left and the Dutch–German left.

The Italian communist left tends to follow Bordigism (though a smaller Damenite current exists) and considers itself to be Leninist, but denounces Marxism–Leninism as a form of bourgeois opportunism materialized in the Soviet Union under Stalin. The Italian current of left communism was historically represented by the Italian Socialist Party and the Communist Party of Italy but today is embodied in the Internationalist Communist Party of Italy, International Communist Party, and the International Communist Current.

The Dutch–German left split from Vladimir Lenin prior to Stalin's rule and supports a firmly council communist and libertarian Marxist viewpoint as opposed to the Italian left which emphasised the need for an international revolutionary party. The Dutch–German current of left communism was historically represented by the Communist Workers' Party of Germany, General Workers' Union of Germany, and the Communist Workers' International.

Left communism differs from most other forms of Marxism in believing that communists should not participate in bourgeois democratic elections, and some argue against participating in trade unions. However, many left communists split over their criticism of the Bolsheviks. Council communists criticised the Bolsheviks for use of the party form and emphasised a more autonomous organisation of the working class, without political parties.

Although she was murdered in 1919 before left communism became a distinct tendency, Rosa Luxemburg has been heavily influential for most left communists, both politically and theoretically. Proponents of left communism have included Herman Gorter, Antonie Pannekoek, Otto Rühle, Karl Korsch, Amadeo Bordiga and Paul Mattick. Other proponents of left communism have included Onorato Damen, Jacques Camatte, and Sylvia Pankhurst. Later prominent theorists are shared with other tendencies such as Antonio Negri, a founding theorist of the autonomist tendency.

Two major traditions can be observed within left communism, namely the Dutch–German current and the Italian current. The political positions those traditions share are opposition to popular fronts, to many kinds of nationalism and national liberation movements and to parliamentarianism.^{[citation needed]}

The historical origins of left communism come from World War I. Most left communists are supportive of the October Revolution in Russia, but retain a critical view of its development. However, some in the Dutch–German current would in later years come to reject the idea that the revolution had a proletarian or socialist nature, arguing that it had simply carried out the tasks of the bourgeois revolution by creating a state capitalist system.

Left communism first came into focus as a distinct movement around 1918. Its essential features were a stress on the need to build a communist party or workers' council entirely separate from the reformist and centrist elements who "betrayed the proletariat", opposition to all but the most restricted participation in elections and an emphasis on militancy. Apart from this, there was little in common between the two wings. Only the Italians accepted the need for electoral work at all for a very short period of time which they later vehemently opposed, attracting criticism from Vladimir Lenin in "Left-Wing" Communism: An Infantile Disorder.