This paper reviews the aetiology of the eating disorders, anorexia nervosa and bulimia nervosa, which is generally thought of as multi-factorial in nature. In recent years with the advent of new bio-technologies interest in the exploration of the contribution of biological, in particular genetic factors to the origins of these disorders has been revived. The challenge for the future is to understand better the relative importance of biological and psychosocial risk-factors and how these factors interact. Moreover, there is a need for a greater appreciation of the developmental perspective in the origins of eating disorders.