Lenin's book “The Childish Disease of ‘Leftism’ in Communism” is an outstanding theoretical work, which summarizes the gigantic historical experience of the Bolshevik Party and the experience of the world communist movement. In his book, Lenin further developed the cardinal problems of Marxism - the doctrine of the dictatorship of the proletariat, the leading role of the Communist Party in the revolutionary struggle and the building of a new society, the position on the correlation between the international and the national in the labor movement, developed the strategy and tactics of the international communist movement in the new historical epoch.