Marxism-Leninism is a term which originated in Stalin's Soviet Union to describe its official ideology, previously known as Marxism. Although they also adhere to Lenin's teachings, the anti-Stalin supporters of Trotsky (Trotskyists), do not use this term, speaking rather about their adherence to Marxism, Leninism and Trotskyism. Stalin, by contrast to Trotsky, did not write a significant body of theoretical work, a Stalinism (the word Stalinism hence refers generally to a style of government, rather than an ideology), but rather adhered officially to the teachings of Marx as revised by Lenin. This orthodoxy of Marxism-Leninism henceforth became a badge of official Communism throughout the world, even after Stalin was discredited in the Soviet Union. The repudiation of Stalin in the Soviet Union and elsewhere led to an anti-revisionist movement, led by the People's Republic of China and Mao Tse-tung in particular, who claimed to represent true Marxism-Leninism in the line of Stalin. Their anti-Stalin opponents (and some pro-Stalin ones, such as Bill Bland in the United Kingdom) disagreed and insisted that Mao was espousing a new ideology, Maoism. Some Mao supporters subsequently acknowledged the important originality of Mao's thought and embraced this term, or the term Marxism-Leninism-Maoism.

Today, the appellation 'Marxist-Leninist' is in use broadly by two groups: those who stand in the legacy of Stalin but either reject Mao or are ambivalent about him (e.g. the Alliance Marxist-Leninist), and the Maoists themselves (e.g. the Communist Party of India (Marxist-Leninist)). Some other groups exist who call themselves Marxist-Leninist but reject Stalin, such as the Communist Party of Great Britain (PCC).

It should further be noted that popular confusion about this complex piece of terminology abounds, and that the appellation 'Marxist-Leninist' is generally taken by lay people, newspapers, etc. for a synonym for Leninism and even for any kind of Marxism.