Foam cells are the characteristic cells of atherosclerosis (Fig. 7.1), playing a central role in all processes from the initial lesion of fatty streaks to the rupture of atheromas, including inflammatory reactions, cell proliferation, cell death, extracellular matrix degradation, and thrombus formation. Therefore, the mechanism of foam cell formation has been a major challenge in atherosclerosis research, but the discovery of the LDL receptor by Goldstein and Brown (1977) was a breakthrough in elucidating this mechanism.