This book is a contribution to the current philosophical discussion on the nature of health and illness. It contains a comparative analysis and reevaluation of four influential contemporary theories in this field. These are the biostatistical theory of Christopher Boorse which represents the mainstream thinking in medicine, and three versions of a holistic and normative understanding of health and illness which are the theories of Lawrie Reznek, K. W. M. Fulford, and Lennart Nordenfelt. In this unusual volume of assessment, Nordenfelt critically reexamines his own theory, and George Khushf and K. W. M. Fulford contribute critical responses.