Diversity and plasticity are hallmarks of mononuclear phagocytes, which are reflected in plaque formation and evolution. Different monocyte subsets, which differentially contribute to plaque infiltration and to atherosclerosis complications, have been identified. Similarly, depending on different environmental signals plaque-associated macrophages can express polarized pro- and antiatherogenic programs by influencing lipid metabolism, inflammatory responses, and plaque stability. Thus, a “macrophage balance” plays a major role in the pathogenesis of atherosclerotic plaques and affects evolution and complications of atherosclerosis.