The International of Proletarian Freethinkers (IPF) was an international atheist 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 Atheists of the USSR, was a mass voluntary organization of Soviet working people that existed from 1925 to 1947. The formation of the League of Militant Atheists 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 Atheists was played by the newspaper "Bezbozhnik" ("The Godless", 1922–1941), around which a broad network of correspondents and readers' circles formed. On their basis, in August 1924 in Moscow, the Society of Friends of the newspaper "Bezbozhnik" (SFB) was formed. In April 1925, the 1st Congress of the SFB took place, at which a unified all-Union anti-religious society was created and adopted the name "League of the Godless"; from the 2nd Congress (1929) it became the League of Militant Atheists. The Central Council of the LMA was continuously headed by E. M. Yaroslavsky.