The International of Proletarian Freethinkers (IPF) was an international atheistic association of workers, founded on July 1, 1925, in the city of Teplice (Czechoslovakia). It included representatives of anti-religious organizations from the USSR, Czechoslovakia, Germany, Austria, the USA, France, Poland, Denmark, Switzerland, Belgium, Sweden, Japan, Bulgaria, India, and others. IPF sections carried out mass anti-religious work among workers, peasants, women, and youth, linking the struggle against religious beliefs with the tasks of the socialist movement. The IPF published the journals "Der Atheist" (1927–33) and "International of Proletarian Freethinkers" (1931–36). In 1936, the IPF merged with the Brussels International of Freethinkers, composed mainly of petty-bourgeois strata, into a single Union of Freethinkers on the platform of a united anti-fascist popular front.
An anti-religious organization in the USSR, the League of Militant Godless of the USSR, was a mass voluntary organization of working people in the USSR that existed from 1925 to 1947. The formation of the League of Militant Godless was an expression of the anti-religious movement that unfolded in the country after the victory of the October Revolution of 1917 and during socialist construction, under the influence of the Communist Party's ideological-educational and cultural-enlightenment work.
A major role in the emergence of the League of Militant Godless was played by the newspaper "Bezbozhnik" ("The Godless", 1922–1941), around which a broad network of correspondents and circles of readers took shape. On this basis, in August 1924 in Moscow, the Society of Friends of the newspaper "Bezbozhnik" (SFB) was formed. In April 1925, the First Congress of the SFB was held, at which a single all-Union anti-religious society was created, adopting the name "League of the Godless"; from the Second Congress (1929) onward it was called the League of Militant Godless. The Central Council of the LMG was continuously headed by E. M. Yaroslavsky.