The Independent Socialist Party (Dutch: Onafhankelijke Socialistische Partij; OSP) was a revolutionary socialist political party in the Netherlands.
The party was founded by a group around Jacques de Kadt and Piet J. Schmidt on March 28, 1932. The group had split from the SDAP after a conflict over the internal opposition publication, the De Fakkel. The moderate leadership of the SDAP banned the publication, in reaction to this the leftwing opposition left the party. It entered in the 1933 elections where at won 27,000 votes and nearly one seat. In 1935 the party merged with the Revolutionary Socialist Party, and formed the Revolutionary Socialist Workers Party.
The OSP was an orthodox Marxist, revolutionary socialist party, which opposed both the authoritarian stalinism of the Communist Party of the Netherlands and the moderate reformism of the Social-Democratic Workers' Party. The party's main goal was the proletarian world revolution, which would replace the capitalist system by a system of workers' councils. In the end this would result in a Communist society where inequality, exploitation and class would be eliminated.