Russian Marxism is the outcome of two distinct traditions, namely, nineteenth-century Russian radicalism and Western European Marxism. In this paper I shall briefly trace its descent from these traditions and try to distinguish those features of it which differentiate it both from the older radicalism and from the Marxism of Marx and Engels. I shall deal in turn with three main topics, the nineteenth-century radical tradition, early Russian Marxism, and finally, Leninism.