Significance: The current literature regarding the effects of the gaseous signal molecule hydrogen sulfide (H₂S) in the gastrointestinal system is reviewed. Bacterial, host and pharmaceutical-derived H₂S are all considered and presented according to the physiological or pathophysiological effects of the gaseous signal molecule. These subjects include the toxicology of intestinal H₂S with emphasis on bacterial-derived H₂S, especially from sulfate-reducing bacteria, the role of endogenous and exogenous H₂S in intestinal inflammation, and the roles of H₂S in gastrointestinal motility, secretion and nociception. Recent Advances: While its pro- and anti-inflammatory, smooth muscle relaxant, prosecretory, and pro- and antinociceptive actions continue to remain the major effects of H₂S in this system; recent findings have expanded the potential molecular targets for H₂S in the gastrointestinal tract. Critical Issues: Numerous discrepancies remain in the literature, and definitive molecular targets in this system have not been supported by the use of competitive antagonism. Future Directions: Future work will hopefully resolve discrepancies in the literature and identify molecular targets and mechanisms of action for H₂S. It is clear from the current literature that the long-appreciated relationship between H₂S and the gastrointestinal tract continues to be strong as we endeavor to unravel its mysteries. Antioxid. Redox Signal. 20, 818–830.