The history and scope of behavioural medicine are briefly outlined and compared with previous attempts to integrate psychological factors in medical practice. Subsequently an attempt is made to clarify the link between physical functioning and behaviour by describing four aspects of behaviour that can be shown to be directly linked to physical functioning: the conditioning of physical responses ; the cognitive processes in the formation of symptoms ; the physiological component of emotions and the behavioural regulation of basic life functions. Through modification of these behavioural variables, behavioural medicine directly influences physical functioning, and, hence, physical health.