Glia are the most abundant cell type in the cortex. In this issue, by combining single-cell RNA-Seq with intersectional lineage analyses, Li et al. demonstrate that mouse cortical oligodendrocytes, astrocytes, and olfactory bulb interneurons are derived from common intermediate progenitors. In the cover image, the brain-like root of the trunk represents the cortical multipotent intermediate progenitor cells (green), which grow into three main branches. The branches represent different types of cells derived from the progenitor cells: oligodendrocytes (orange), astrocytes (pink), and olfactory bulb interneurons (blue). See pages 440–460. (Cover art by Dr. Fei Dong and LinYang).