Atherosclerosis is the pathophysiological basis of a variety of cardiovascular diseases, with monocytes/macrophages being a key cell type that participates in the initiation of vascular inflammation, the formation, progression and rupture of atherosclerotic plaques. In recent years, with the rapid development of single-cell sequencing technology, the high heterogeneity and plasticity of mononuclear macrophages in plaques have been gradually elucidated. This article reviews the latest monocyte/macrophage subtypes identified in patients and mouse models of atherosclerosis through single-cell sequencing technology, summarizes their markers, functional heterogeneity, and underlying mechanisms, with the aim of providing more precise directions for the diagnosis and treatment of atherosclerosis.