Nature, Published online: 26 March 2025; doi:10.1038/d41586-025-00872-zMapping the density, molecular features and energy-transformation capacity of cell organelles called mitochondria in the brain reveals region- and cell-type-specific variability that tracks with evolutionary patterns. Correlations between mitochondrial and brain-imaging metrics could enable future non-invasive explorations of mitochondrial bioenergetics in the brain in health and disease.