"Left-Wing" Communism: An Infantile Disorder (, ) is a work by Vladimir Lenin attacking assorted critics of the Bolsheviks who claimed positions to their left. Most of these critics were proponents of ideologies later described as left communism. The book was written in 1920 and published in Russian, German, English and French later in the year. A copy was then distributed to each delegate at the 2nd World Congress of the Comintern, several of whom were mentioned by Lenin in the work. The book is divided into ten chapters and an appendix.

Lenin's manuscript was subtitled "A Popular Exposition of Marxist Strategy and Tactics", but this was not applied to any edition brought out during his lifetime.

Bolsheviks

Lenin points out that the Russian Revolution has considerable international significance and criticises the leaders of the Second International, including Karl Kautsky, for failing to recognize the international relevance of soviet power as a revolutionary model. To illustrate their move away from revolutionary politics, he supplies a quote from a 1902 work of Kautsky which concludes that "Western Europe is becoming a bulwark of reaction and absolutism in Russia". Lenin asserts that in a war against the bourgeoisie "iron discipline" is an "essential condition". He continues by describing the circumstances that resulted in the Bolsheviks' successful assumption of state power in Russia.

The third chapter divides the history of Bolshevism into the "years of preparation of the revolution" (1903–1905), the "years of revolution" (1905–1907), the "years of reaction" (1907–1910), the "years of rise" (1910–1914), the "first imperialist world war" (1914–1917) and the "second revolution in Russia". He describes the changing circumstances for revolutionaries in Russia and the reaction of the Bolsheviks to them.

Lenin describes the enemies of the working class as opportunists, petty-bourgeois revolutionaries which he links to anarchism; and the "Left" Bolsheviks (expelled from the Bolshevik group in 1909), whom he links with those who criticised the Peace of Brest-Litovsk. He ends by criticizing the Mensheviks, Socialist Revolutionaries and members of the Socialist International who were prepared to compromise with the German leaders in defence of a capitalist system.

"Left-wing" communism in Germany

The fifth, sixth and seventh chapters discuss a section of the Communist Party of Germany which split between the writing of the document and its publication to form the Communist Workers Party of Germany (KAPD). As an example, he takes Karl Erler's article "The Dissolution of the Party". Lenin criticised the group's anti-trade union attitude, their anti-parliamentarism and Erler's proposal of a dictatorship of the masses as a counterpoint to the "dictatorship of the party" he claims the Russian Revolution has led to.

Lenin notes that the Russian Communist Party (Bolsheviks) rely on the Russian trade unions and that a reactionary labour aristocracy is inevitable, but must be fought within the union movement. In contrast to the KAPD, he holds that so long as much of the proletariat holds illusions in parliaments, communists must work inside such reactionary organisations. Lenin then compares the anti-parliamentarism of the Dutch left and that of Amadeo Bordiga.

Lenin then criticises the slogan "no compromises", noting that the Bolsheviks had made many compromises in their history. He believes that this is using theory as dogma, rather than as a "guide to action". Lenin also criticises National Bolshevism and some leftists for not recognising the Treaty of Versailles.

"Left-wing" communism in Great Britain

Lenin critiques the Workers Socialist Federation's opposition to parliamentary action and in particular to affiliation to the Labour Party through texts written by Sylvia Pankhurst and Willie Gallacher. He proposes that all the main socialist groups in the country should form a Communist Party of Great Britain and that they should offer an electoral coalition with Labour. He concludes that the party would gain whether or not Labour accepted the offer. In a famous turn of phrase, he says that they should support Labour General Secretary Arthur Henderson "in the same way as the rope supports a hanged man".