This chapter reviews the current research on involvement of psychological processes in functional gastrointestinal disorders (FGIDs), with specific focus on how future research can address limitations of current understanding. FGIDs have strong connections with mental state in general and aspects of mental health in particular. FGIDs, particularly irritable bowel syndrome (IBS) have strong associations with a range of psychological traits, including diagnosable psychological pathology. Evidence demonstrates that a number of maladaptive psychological traits are consistently associated with FGIDs. A number of maladaptive psychological traits are present in higher levels in IBS than healthy individuals, including neuroticism, anxiety and depression. Psychological therapies have reproducible, medium-sized effects on GI symptoms, and associated health-related quality-of-life outcomes. The biopsychosocial model demonstrates the bidirectional relationship between psychological distress and FGID symptoms. Since psychological therapies are known to act upon psychological distress, this decrease in distress may act to decrease FGID symptoms.