"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.

The 2nd World Congress of the Communist International was a gathering of approximately 220 voting and non-voting representatives of communist and revolutionary socialist political parties from around the world, held in Petrograd and Moscow from July 19 to August 7, 1920. The 2nd Congress is best remembered for formulating and implementing the 21 Conditions for membership in the Communist International.