Nitric oxide is an intracellular and intercellular messenger with important functions in a number of physiologic and pathobiologic processes within gastroenterology and hepatology, including gastrointestinal tract motility, mucosal function, inflammatory responses, gastrointestinal malignancy, and blood flow regulation. Since the broad review of this topic in Gastroenterology more than 10 years ago, a number of advances have been made in the area of NO biology and its relevance to the gastrointestinal system. The aim of this review is to focus on our expanded understanding of the role NO plays in human gastrointestinal and hepatic physiology and disease processes by drawing on data from relevant in vitro and animal models as well as observational human studies.