Series comprises correspondence, memoranda, grey literature, ephemera, financial records, reference files, and other documents relating to the activities of the League for Socialist Action / Ligue Socialiste Ouvrière, the largest Trotskyist organization ever active in Canada. Documents LSA/LSO interventions in the labour movement and the NDP as well as its electoral campaigns, its involvement with the Fair Play for Cuba Committee, its publishing and educational programmes, and its participation in various mass movements, including the women's movement, the anti-war movement, and the student movement. Also sheds light on the local activities of various LSA/LSO branches, the organization's relations with the Socialist Workers Party and other foreign Trotskyists, and the development of factionalism as the LSA/LSO underwent unprecedented growth and grappled with a number of highly contentious issues, such as the Quebec question, Canadian nationalism, and the appropriate orientation to the New Democratic Party. As well, includes substantial documentation pertaining to other left-wing organizations in Canada. Records are arranged in thirty-three blocks of files: Conventions, Plenums, and Political Committee Records; Branch Records; Ottawa Branch; Financial, Publishing, and Membership Records; Educational Records; Women's Liberation and Abortion; Anti-War Movement; War Measures Act; Municipal and Other Elections; Teamsters Local 938; Trade Unions; Teachers; Students; Anti-Apartheid; Gay Liberation; Immigration and Racism; CCF, NDP, and Waffle; Cuba; United Secretariat, Fourth International; International Correspondence and Other Files; Latin American and Caribbean; Native Rights; Quebec; Other Left-Wing Political Organizations; Revolutionary Marxist Group; Tendencies; Anti-Nuclear; Camp Poundmaker; Summer School Classes; Ross Dowson; Art Young; Tours; and Central Office - Miscellaneous Files.