Peroxisome Proliferator-Activated Receptors (PPARs), members of the steroid hormone nuclear receptor superfamily, act as ligand-activated transcription factors controlling the expression of specific target genes. Known PPAR isoforms include PPAR gamma, important in adipogenesis and lipid metabolism, PPAR alpha, implicated in fatty acid metabolism, and PPAR delta, about which the least is known. Recent work implicates PPAR alpha and gamma in vascular biology and atherosclerosis, and will be reviewed here. Such effects may have clinical implications given PPAR agonists in use as pharmacologic agents (eg, thiazolidinediones as insulin sensitizers [gamma] and fibric acids as lipid lowering agents [alpha]).