Transitional neuronal layers are a hallmark of the prenatal and neonatal brain yet their contribution to the development of higher functions is not clear. Evidence accumulated over the last 3 decades shows that early connectivity and functional activity start in a transitional layer called the subplate zone (SPZ). The SPZ is host to a heterogeneous population of neurons and its evolutionary complexity peaked in the human brain. In this issue of Cerebral Cortex, three reports (Hoerder-Suabedissen et al., 2008; McKellar and Shatz, 2008; Moore et al., 2008) present new data and evidence in three species (mouse, rat, human) as to the function of the SPZ, to the heterogeneity of its cellular composition, and to the genetic basis of its development.