The anti-Stalinist left encompasses various kinds of left-wing political movements that oppose Joseph Stalin, Stalinism, neo-Stalinism and the system of governance that Stalin implemented as leader of the Soviet Union between 1924 and 1953. This term also refers to those that opposed Joseph Stalin and his leadership from within the Communist movement, such as Leon Trotsky and the party's Left Opposition.

In recent years, the term may also refer to left and centre-left wing opposition to dictatorship, cult of personality, totalitarianism and police states, all being features commonly attributed to Marxist-Leninist regimes that took inspiration from Stalinism such as the regimes of Kim Il Sung, Enver Hoxha and others, including in the former Eastern Bloc. Some of the notable movements within the anti-Stalinist left have been Trotskyism and Titoism, anarchism and libertarian socialism, left communism and libertarian Marxism, the Right Opposition within the Communist movement, Eurocommunism, ultra-leftism, democratic socialism and social democracy.

A large majority of the political left was initially enthusiastic about the Bolshevik Revolution in the revolutionary era. In the beginning, the Bolsheviks and their policies received much support because the movement was originally painted by Lenin and other leaders in a libertarian light. However, as more politically repressive methods were used, the Bolsheviks steadily lost support from many anarchists and revolutionaries. Prominent anarchist communists and libertarian Marxists such as Sylvia Pankhurst, Rosa Luxemburg, and Emma Goldman were among the first left-wing critics of Bolshevism.

Rosa Luxemburg was heavily critical of the methods that Bolsheviks used to seize power in the October Revolution claiming that it was "not a movement of the people but of the bourgeoisie". Primarily, Luxemburg's critiques were based on the manner in which the Bolsheviks suppressed anarchist movements. In one of her essays published titled "The Nationalities Question in the Russian Revolution", she explains:

To be sure, in all these cases, it was really not the "people" who engaged in these reactionary policies, but only the bourgeois and petit bourgeois classes, who – in sharpest opposition to their own proletarian masses – perverted the "national right of self-determination" into an instrument of their counter-revolutionary class policies.

Because of her early criticisms toward the Bolsheviks, her legacy was vilified by Stalin once he rose to power. According to Trotsky, Stalin was "often lying about her and vilifying her" in the eyes of the public.

The relations between the anarchists and the Bolsheviks worsened in Soviet Russia due to the suppression of movements like the Kronstadt rebellion and the Makhnovist movement. The Kronstadt rebellion (March 1921) was a key moment during which many libertarian and democratic leftists broke with the Bolsheviks, laying the foundations for the anti-Stalinist left. The American anti-Stalinist socialist Daniel Bell later said:

Every radical generation, it is said, has its Kronstadt. For some it was the Moscow Trials, for others the Nazi-Soviet Pact, for still others Hungary (The Raik Trial or 1956), Czechoslovakia (the defenestration of Masaryk in 1948 or the Prague Spring of 1968), the Gulag, Cambodia, Poland (and there will be more to come). My Kronstadt was Kronstadt.