The Workers' Socialist Movement (Spanish: Movimiento Socialista de los Trabajadores, MST) is a Puerto Rican democratic socialist revolutionary organization, formed in 1982 and dedicated to the self-organization and self-emancipation of the working-class in Puerto Rico, as well as international solidarity with the workers struggles worldwide.

This is both a result of a need for dedication and trust building from cadres, and as a way to prevent the state repression that has plagued other organizations in Puerto Rico.

Influenced by the Cuban Revolution, especially Che Guevara, the Chinese Revolution and Mao Zedong, and a number of similar revolutionary experiences worldwide, the MST began to replace the declining Puerto Rican Socialist Party as the predominant far-left group in Puerto Rico.

Among its supporters are Rafael Feliciano Hernández twice-elected leader of the Teachers' Federation of Puerto Rico, on an openly socialist platform; Victor Rodriguez, student leader and spokesman of the UJS in the University of Puerto Rico at Rio Piedras; Pedro Colon Almenas, former political prisoner.

It is also visible in the struggle to call attention to the untried murder case of MSP founding member and Cuban exile Carlos Muñiz Varela, and the attempts on the part of the government to repress protests against the continued coverup in that case, including the recent homage paid for by the Legislature to suspected intellectual author of Muñiz's murder, Julio Labatud.