The rhetoric of "needs" has been used to legitimate all major turns in UK health policy since 1936. This study identifies the ethical, policy and technical issues arising from the concept of needs. In the first part a theory of needs is developed, which takes into account both the philosophical traditions and the practical problems arising in daily health care. In the second part, health systems throughout the world are described and compared, addressing ethical as well as economical questions. This work's interdisciplinary approach should make it useful reading not only for those interested in or employed in the health care sector but also students of philosophy.