In the 21th century we can observe a return to Marx, particularly in the circles of New Left. A critical approach to the legacy of Karl Marx implies a readiness to revise or even reject the false or no longer valid propositions of Marx in order to be able to confront his legacy with the current state of contemporary science. Some of his views have already been definitely rejected (particularly the theory of revolution and of the dictatorship of proletariat). But a part of his contribution remains valid: (1) the philosophy of praxis, i.e. a theory oriented toward a social change, and (2) the sociological theory that interprets politics in terms of class interests.