The early steps in corticogenesis are decisive for the correct unfolding of neurogenesis, neuronal migration and differentiation under tight genetic control. In this monograph, the author outlines the main events in human preplate formation according to their timetable of appearance and the expression of developmentally relevant gene products. Also examined are the gradual transformation of the preplate into the cortical plate, and the establishment of the transient compartments of the foetal cortical wall.