The Rome IV criteria refer to functional gastrointestinal conditions as "Disorders of Gut-Brain Interaction". These conditions are involved in an estimated 40% of patient visits to gastroenterologists. Naturopathic functional diagnosis and individualized treatment are uniquely suited for good outcomes with these disorders. In Functional Gastroenterology, Steven Sandberg-Lewis, ND, DHANP, draws on skills and knowledge he has built during four decades of Naturopathic practice and teaching. He articulates clinical pearls and presents a thorough review of the relevant published research. This text focuses on the underlying causes of functional GI disorders as well as their diagnosis, treatment and management.