This discussion of concepts can be given a degree of coherence by reference to theoretical models of disease and its consequences. Unlike conceptual frameworks, which consist of a list of health domains, these theoretical models link those domains in a causal sequence and identify intervening variables which mediate their relationships. Although there are a number of such models, I would like to confine my comments to one recently specified by Wilson and Cleary (Figure Chapter 2.3). This model is a useful one in that it encompasses disease, health and the quality of life, makes explicit the main causal relationships between them and allocates a mediating role to personal characteristics and the characteristics of the environment in which an individual lives.