Among vertebrates, the ventral part of the telencephalon called the subpallium presents common basic developmental, hodological, neurochemical and functional features. It is genetically specified by expression of Dlx genes; its progenitor zones contribute a huge variety of neuronal cell types throughout the telencephalon; it is the origin and substrate of multiple and complex migration and navigation pathways during embryogenesis; and its derivatives, i.e. the basal ganglia and the amygdaloid complex, are highly conserved through evolution. Comparative developmental studies point to a largely common basic plan to generate the subpallium in vertebrates, including comparable progenitor domains and similar migratory cellular movements. In the course of telencephalic evolution however, slight variations have occurred, and the subpallium has probably represented a source for significant novelties and diversification in vertebrate forebrain anatomy and physiology.