Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors of the nuclear hormone receptor super-family, which includes the steroid, retinoid, and thyroid hormone receptors. The PPARs can be activated by fatty acids and their eicosanoid metabolites, and have until recently been considered primarily to regulate genes involved in glucose and lipid homeostasis. In the past year there has been an explosive increase in research implicating PPARgamma in macrophage biology, cell cycle regulation, and atherosclerosis. This review describes recent insights into the role of PPARgamma in the macrophage lineage, and its potential function in the regulation of inflammatory responses and atherosclerosis.