Hominin evolution is characterized by two main trends, transition to bipedality and increase in brain size. Fossil evidence shows that both trends had a major impact on the structure and function of the hominin skull. This chapter asks how evolutionary modification of the cranial ontogenetic program led to morphological reorganization of the hominin skull and ultimately to hominin cranial diversity. Three major mechanisms of evolutionary developmental reorganization are proposed: modified prenatal development of the cranial base and face reflects adaptation to bipedality; high rates of neurocranial growth during early postnatal ontogeny are essential to attain large brain sizes; taxon-specific modification of facial development reflects dietary adaptation and-in the genus Homo-a general trend toward neoteny.