Throughout the last decade, the field of clinical psychology has expanded dramatically. Clinical psychologists are involved in the treatment and research of a wider range of problems and disorders than they have ever been before. Evidence has been rapidly ac cumulating regarding the role of psychological variables and stress in the etiology and maintenance of a range of medical and psychiatric disorders. New models of psy chotherapy have been developed and refined, and the specific efficacy of psychother apeutic interventions for an increasing number of disorders (or sUbtypes of disorders) has been documented. However, concurrent with research that demonstrates the impact of psychosomatic factors in various disorders and the efficacy of psychological or psychosocial interven tions, dramatic progress has been made with regard to the investigation of biological factors that may mediate certain disorders. That physical factors may underlie many in stances of psychiatric illness has been repeatedly demonstrated. Also, the efficacy of so matic treatments for different disorders, or for subtypes of disorders, has been reported with increasing methodological rigor.