Common personal experience readily informs us that emotions can influence gastrointestinal function. Over the last 200 years, this interaction has been interrogated with increasingly sophisticated techniques across a diverse range of scientific and clinical disciplines. Bottom‐up processing from gut‐to‐brain and top‐down autonomic, immune and neuroendocrine mechanisms in brain‐to‐gut signaling constitutes a bi‐directional circuit of communication, known as the brain gut axis. The brain gut axis itself comprises a diverse array of component parts as well as those that influence its function. This chapter provides a review of functional anatomy and physiology of the brain gut axis and examine both the bottom‐up and top‐down interactions, encompassing the role of the GI microbiome, autonomic nervous system and the hypothalamic pituitary adrenal axis. Knowledge emanating from these interactions has informed understanding of appetite/satiety regulation and how alterations can lead to clinical syndromes.