This chapter reviews the effect of stress on gastrointestinal (GI) physiology, the evidence supporting dysregulation of stress response systems in functional gastrointestinal disorders (FGIDs), and describes how this informs therapeutic options. The 'allostasis' describes the process by which stability is maintained in the face of stress. Systems involved in maintaining allostasis include the autonomic nervous system (ANS) and hypothalamic-pituitary-adrenal (HPA) axis, among others. The ANS and HPA axis are two principal output systems of the general stress response. The effect of stress on gut function and sensation results from alterations in the brain-gut axis. Early life stress or adverse childhood experiences (ACEs), which have emerged as an important predictor of a variety of diseases and poor health outcome overall, are also associated with the development of IBS. ACEs are common risk factors for psychiatric disorders and FGIDs, but ACEs have been associated with a wide variety of diseases and negative health outcomes.