Alex Callinicos places Althusser's work in the context of the two main traditions of Marxist philosophy, Engels and the orthodox "dialectical materialism" of the Second International, Lukács and the Hegelian Marxism of the 1920's. He provides an introduction to the entire range of Althusser's ideas and traces, for the first time in English, their development and transformation. The result is an attempt to judge Althusser, not simply as a philosopher, but as a Marxist.