Endothelial dysfunction is an important component in the pathogenesis of atherosclerosis. The ability to assess the endothelium in a meaningful manner has been the subject of intense investigation over decades. Since the function of endothelial cells is a gauge of vascular health, assessment of vascular function is emerging as a useful tool for predicting cardiovascular risk and as a surrogate outcome measure for cardiovascular reduction intervention studies. This review highlights techniques for assessing endothelial function, focusing on a novel method of determining peripheral vascular reactivity via arterial tonometry.