This lecture covers the early regionalization of the brain, starting with the three primary brain vesicles and the development of prosencephalon, mesencephalon, and rhombencephalon. It then progresses to the finer regionalizations, discussing the complex anatomy and the availability of gene expression and anatomical atlases to interpret these processes correctly. The differentiation and migration of cells in the neocortex, striatum, and ganglionic eminences are also explored.