Peroxisome proliferator-activated receptors (PPAR) are ligand-activated transcription factors which form a subfamily of the nuclear receptor gene family. PPAR activators have effects on both metabolic risk factors and on vascular inflammation related to atherosclerosis. PPAR have profound effects on the metabolism of lipoproteins and fatty acids. PPARα binds hypolipidemic fibrates, whereas PPARγ has a high affinity for antidiabetic glitazones. Both PPAR are activated by fatty acids and their derivatives. Activation of PPARα increases the catabolism of fatty acids at several levels. In the liver, it increases uptake of fatty acids and activates their β-oxidation. The effects that PPARα exerts on triglyceride-rich lipoproteins is due to their stimulation of lipoprotein lipase and repression of apolipoprotein CIII expression, while the effects on high-density lipoproteins depend upon the regulation of apolipoproteins AI and AII. PPARγ has profound effects on the differentiation and function of adipose tissue, where it is highly expressed. PPAR are also expressed in atherosclerotic lesions. PPAR are present in vascular endothelial cells, smooth muscle cells, monocytes, and monocyte-derived macrophages. Via negative regulation of nuclear factor-κB and activator protein-1 signalling pathways, PPARα inhibits expression of inflammatory genes, such as interleukin-6, cyclooxygenase-2, and endothelin-1. Furthermore, PPARα inhibits expression of monocyte-recruiting proteins such as vascular cell adhesion molecule (VCAM)-1 and induces apoptosis in monocyte-derived macrophages. PPARγ activation in macrophages and foam cells inhibits the expression of activated genes such as inducible nitric oxide synthase, matrix metalloproteinase-9 and scavenger receptor A. PPARγ may also affect the recruitment of monocytes in atherosclerotic lesions as it is involved in the expression of VCAM-1 and intracellular adhesion molecule-1 in vascular endothelial cells. The involvement of PPAR in atherosclerosis, a disease with a chronic inflammatory character, suggests that they may play a role in other inflammatory-related diseases as well.