The totality of epidemiologic evidence demonstrates a high burden of subclinical carotid disease in middle-aged and elderly men and women. This chapter reviews the epidemiology of carotid artery atherosclerosis, including its distribution, determinants and risks conferred by its presence. High-resolution imaging modalities are now available to provide reproducible, quantitative assessment of the degree of luminal obstruction or wall disease of the carotid artery. High-resolution B-mode imaging ultrasonography is useful for detection of the degree of luminal stenosis or of intimal medial thickness (IMT) of the common carotid artery, carotid bulb, and the internal carotid artery. Carotid stenosis as well as internal carotid IMT and common carotid IMT are each associated with prevalent cardiovascular disease. Elegant clinical-pathological studies have been performed on humans with carotid artery segments that were first imaged by magnetic resonance and subsequently removed by carotid endarterectomy.