SUMMARYWe applied single-cell RNA sequencing to profile genome-wide gene expression in about 9,400 individual cerebellar cells from the mouse embryo at embryonic day 13.5. Reiterative clustering identified the major cerebellar cell types and subpopulations of different lineages. Through pseudotemporal ordering to reconstruct developmental trajectories, we identified novel transcriptional programs controlling cell fate specification of populations arising from the ventricular zone and the anterior rhombic lip, two distinct germinal zones of the embryonic cerebellum. Together, our data revealed cell-specific markers for studying the cerebellum, important specification decisions, and a number of previously unknown subpopulations that may play an integral role in the formation and function of the cerebellum. Importantly, we identified a potential mechanism of vermis formation, which is affected by multiple congenital cerebellar defects. Our findings will facilitate new discovery by providing insights into the molecular and cell type diversity in the developing cerebellum.