In introducing this Special Issue on Clinical Health Psychology, we start by offering some definitions with the aim of clarifying, or at least presenting, some of the existing confusion. We have defined health psychology as the study of psychological and behavioural processes in health, illness and health care' (Johnston, 1994). Belar and Deardorff (1995) see clinical health psychology as a merging of clinical psychology with its focus on the assessment and treatment of individuals in distress . . . and the content field of health psychology' (p. 1) and characterize it using Millon's (1982) definition: `The application of knowledge and methods from all substantive fields of psychology to the promotion and maintenance of mental and physical health of the individual and to the prevention, assessment, and treatment of all forms of mental and physical disorder in which psychological influences either contribute to or can be used to relieve an individual's distress and dysfunction' (Millon, 1982, p. 9).
The focus in health psychology is on physical health problems (Belar, 1997). Definitions of other overlapping areas such as behavioural medicine and psychosomatic medicine are discussed in some detail by Belar and Deardorff (1995). Health psychology is distinguished by its base in the discipline of psychology and the resultant theoretical perspectives, models of measurement and designs of interventions.