The articles in this special issue form three overlapping themes: papers concerned with language development, other aspects of cognition, and interpersonal relations and personality. The papers provide strong evidence of the importance of the study of individuals with neurodevelopmental genetic disorders for enhancing the understanding of the complex manner in which initial genetic differences impact on both behavior (performance) and processing strategies from infancy through adulthood. Much work remains to be done, not only from a psychological or a biological perspective but, most importantly, from an integrated psychological-biological perspective. The hope is that these articles will motivate future studies informed by the genetic-developmental approach both on Williams syndrome and on other neurodevelopmental genetic disorders.