The physiology of the mesenteric circulation is described emphasizing important aspects of microcirculatory function and the factors which regulate blood flow to the bowel. Next, the pathophysiology of intestinal ischemia is considered with special focus on the disturbed mechanisms involved in ischemic disorders, such as active oxidant formation and inhibition of intrinsic protective systems. The histopathology of small intestinal and colonic ischemia and infarction is described. Finally, clinical issues are addressed including the diagnostic challenge and the management of these life-threatening disorders.