The basic discoveries underlying Marx's critique of political economy - labour power, surplus value, use value - are all in some way built upon the concept of need. From Marx's varying and passing interpretations of a theory of need, Agnes Heller unravels the main tendencies and demonstrates the importance which Marx attached to the "restructuring" of a system of needs going beyond the purely material. She also brings out those aspects, especially the idea of "radical needs" which point to revolutionary activity and to the project which Marx could only foresee but which for us today is of real urgency: the "society of associated producers". Thus Agnes Heller's study is not only the first full presentation of a fundamental aspect of Marx, but the basis for a discussion of the utmost contemporary relevance.