In the last decade, an increasingly sophisticated understanding of the pathogenesis of atherosclerosis and its cardiovascular consequences has emerged. The characteristics of the unstable atherosclerotic plaque, the substrate for the majority of acute coronary events, have been well defined: mild-to-moderate stenosis, a lipid-rich pool, few smooth muscle cells, a friable fibrous cap, and macrophage infiltration. Lipid modification, an important cardiovascular risk reduction strategy, induces a number of effects at the vascular level that may contribute to the clinical benefits seen in large-scale, prospective prevention trials. New developments in imaging technologies may afford improved opportunities to visualize the at-risk plaque and may provide new insights into the optimal management of the unstable plaque.