Atherosclerosis is a disease of muscular arteries resulting from the progressive accumulation of cells, lipids, and collagen. When sufficient deposition of these abnormal components has occurred, the vascular lumen is narrowed leading to thrombosis, embolism, acute occlusion, or aneurysm formation. Medical complications with significant morbidity and mortality are associated with these vascular lesions and include ischemic heart disease, myocardial infarction, stroke, and gangrene of the extremities. Epidemiologic studies of humans with disease have contributed to the identification of risk factors for the development of atherosclerosis. And, various models including transgenic animals have been utilized to better understand the contribution of various gene products in this complex disorder.