The functional gastrointestinal disorders (FGID) are the most frequent conditions seen in gastroenterology practice and comprise a major portion of primary care. Psychosocial factors are important in these disorders with regard to: (1) their effects on gut physiology; (2) their modulation of the symptom experience; (3) their influence on illness behavior; (4) their impact on outcome; and (5) the choice of the therapeutic approach. This paper provides a review and consensus of the existing literature by gastroenterologists, psychiatrists, psychologists, physiologists, and health services investigators. Evidence is provided to support the biopsychosocial model as a basis for understanding and treating these disorders, and epidemiological and clinical information on the relations of psychosocial factors to gut physiology, symptom presentation, health behavior, and outcome is offered. Features of motility, personality, abuse history, health concerns, and treatment-seeking differ between patients with FGID and healthy controls, but they are not specific to FGID. They occur in other patients with chronic medical conditions and/or psychiatric disorders. Review of treatment trials indicates clear support for psychotherapeutic treatments, especially in the long term, as well as some evidence for the benefit of antidepressants in FGID, even in the absence of improvements in mood.