2nd World Congress of the Comintern in the context of Sergey Zorin

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.

In the political terminology of the former Soviet Union, the state of socialist orientation (Russian: Страны социалистической ориентации, romanized: Strany sotsialisticheskoy oriyentatsii, lit. 'countries of socialist orientation'), also called socialist-leaning state and socialist-oriented state, were the post-colonial Third World countries which the Soviet Union recognized as adhering to the ideas of socialism in the Marxist–Leninist understanding. As a result, these countries received significant economic and military support. In Soviet press, these states were also called "countries on the path of the construction of socialism" (Russian: страны, идущие по пути строительства социализма, romanized: strany, idushchiye po puti stroitel'stva sotsializma) and "countries on the path of the socialist development" (Russian: страны, стоящие на пути социалиcтического развития, romanized: strany, stoyashchiye na puti sotsialicticheskogo razvitiya). All these terms meant to draw a distinction from the true socialist states (in Marxist–Leninist understanding).

The use of the term was partly a result of a reassessment of national liberation movements in the Third World following World War II, widespread decolonization and the emergence of the Non-Aligned Movement as well as Nikita Khrushchev's Secret Speech to the 20th Congress of the Communist Party of the Soviet Union and the de-Stalinization of Soviet Marxism. The discussion of anti-colonial struggle at the 2nd World Congress of the Comintern in 1920 had been formulated in terms of a debate between those for an alliance with the anti-imperialist national bourgeoisie (initially advocated by Vladimir Lenin) and those for a pure class line of socialist, anti-feudal as well as anti-imperialist struggle (such as M. N. Roy). The revolutions of the post-war decolonization era (excepting those led by explicitly proletarian forces such as the Vietnamese Revolution), e.g. the rise of Nasserism, were initially seen by many communists as a new form of bourgeois nationalism and there were often sharp conflicts between communists and nationalists. However, the adoption of leftist economic programs (such as nationalization and/or land reform) by many of these movements and governments, as well as the international alliances between the revolutionary nationalists and the Soviet Union, obliged communists to reassess their nature. These movements were now seen as neither classical bourgeois nationalists nor socialist per se, but rather offering the possibility of "non-capitalist development" as a path of "transition to socialism". At various times, these states included Algeria, Angola, Egypt, Ethiopia, India, Libya, Mozambique, South Yemen and many others.

The Twenty-one Conditions, officially the Conditions of Admission to the Communist International, are the conditions, most of which were suggested by Vladimir Lenin, to the adhesion of the socialist parties to the Third International (Comintern) created in 1919. The conditions were formally adopted by the Second Congress of the Comintern in 1920.