The concept of a number of ‘psychosomatic disorders’ (e.g. peptic ulcer, rheumatoid arthritis) used to imply that psychological and social variables were important only in certain, distinct disorders. This narrow approach has been replaced by a broader concept of ‘psychosomatic research’, namely, the concurrent study of biological, psychological and social variables in health and disease (World Health Organization, 1964). This chapter illustrates how the Life Events and Difficulties Schedule (LEDS) has been invaluable in providing a reliable and valid measure of social variables. The chapter is divided into sections concerning the aetiology of two major forms of disorders: first, patients presenting with medically unexplained symptoms, and second, recognised physical illnesses with clear pathological changes. The chapter indicates how psychological and social variables are now being considered alongside biological ones in terms of aetiology and course of disorder.