This chapter reviews the epidemiology and aetiology of functional gastrointestinal disorders (FGIDs) and the need for integrative treatment. FGIDs are disorders of brain-gut communication. The Rome IV diagnostic criteria identify more than 40 adult and paediatric FGIDs, including well-known disorders, such as irritable bowel syndrome (IBS) and functional constipation, as well as lesser known disorders, such as functional gallbladder disorder and levator ani syndrome. FGIDs are common: they affect about 1 in 4 children and 1 in 3 adults. The three most common adult FGIDs were functional dyspepsia, functional constipation and irritable bowel syndrome. Psychiatric disorders, in particular anxiety and depression, are increased in patients with FGID. The most commonly studied psychological therapies for FGIDs include cognitive behavioural therapy (CBT), hypnosis and biofeedback. Psychological treatments should ideally be offered as part of integrative care. This implies a gastroenterologist and psychologist working together to create a comprehensive treatment plan.