Single-cell RNA sequencing and spatial transcriptomics have revealed that atherosclerotic plaques contain highly heterogeneous populations of macrophages, T cells, B cells, smooth muscle cells, and dendritic cells — each with distinct inflammatory and metabolic states. A key finding is that vascular smooth muscle cells can phenotypically switch into macrophage-like "foam cells" that drive plaque instability. These single-cell maps are now being used to identify which specific cell states are most dangerous and which could be targeted therapeutically, a level of resolution that population-level bulk RNA sequencing could never provide.