The prostanoids are a family of lipid mediators generated by the action of cyclooxygenase on a 20-carbon unsaturated fatty acid, arachidonic acid. Prostanoids are generated widely in response to diverse stimuli and, acting in a paracrine or autocrine manner, play important roles in normal physiology and disease. This review summarizes the current knowledge on prostanoid generation and the roles of individual mediators, their biosynthetic pathways, and their receptors in health and disease.