The Fourth International (FI) is the communist international organisation consisting of followers of Leon Trotsky, or Trotskyists, with the declared goal of helping the working class bring about socialism and work toward international communism. The Fourth International was established in France in 1938: Trotsky and his supporters, having been expelled from the Soviet Union, considered the Comintern or Third International to have become "lost to" Stalinism and incapable of leading the international working class to political power. Thus, Trotskyists founded their own, competing "Fourth International".

The Fourth International (FI), founded in 1938, is a Trotskyist international. In 1963, following a ten-year schism, the majorities of the two public factions of the Fourth International, the International Secretariat and the International Committee, reunited, electing a United Secretariat of the Fourth International. In 2003, the United Secretariat was replaced by an Executive Bureau and an International Committee, although some other Trotskyists still refer to the organisation as the USFI or USec.

Background

The ISFI was the leadership body of the Fourth International, established in 1938. In 1953 many prominent members of the International, and supported by the majority of the Austrian, British, Chinese, French, New Zealand and Swiss sections together with the U.S. Socialist Workers Party organized against the views of Michel Pablo, a central leader of the ISFI who successfully argued for the FI to adapt to the growth of the social democratic and communist parties. This led to disagreements between supporters of the ISFI and those parties on how to build revolutionary parties. These tensions developed into a split, leading to the suspension of those parties which had formed the International Committee of the Fourth International (ICFI) late in November 1953.

The Fourth International (identified here by its major theoretical magazine "La Verite") was established as an "International Centre (or Center) of Reconstruction" by co-thinkers of Pierre Lambert, in 1981 who argued that the post-war political evolution of the Fourth International under the leadership of Michel Pablo and Ernest Mandel had taken the FI away from the ideas of its founder, Leon Trotsky. In the opinion of Lambert and his co-thinkers, the FI needed to be reconstructed. In 1993, they formed a new International, which they describe as the Fourth International. It is, by the number of sections, the Trotskyist tendency in the second largest number of countries.

The Fourth International's (La Verite) roots lie in the Organising Committee for the Reconstruction of the Fourth International (OCRFI), which was established in 1972. It formed a short-lived bloc with Nahuel Moreno's tendency. A Parity Committee which operated in 1979 1980 produced Forty Theses of agreements between the tendencies led by Moreno and Lambert. On that basis, the Fourth International (International Committee) (FI[IC]) was founded in 1980. However, the convergence decelerated because of Lambert's support for the government of Socialist Party (France) and French Communist Party without capitalist ministers, a traditional position of French Trotskyism going back before the death of Trotsky. Moreno's supporters boycotted a General Council of the FI(IC) in the Autumn of 1981 whereupon Lambert declared a split: Moreno's supporters formed the International Workers League; at a meeting on 21–23 December 1981 Lambert's supporters formed the "Fourth International - International Centre of Reconstruction", or ICR.