Autism and Asperger syndrome are diagnostic entities in a family of neurodevelopmental disorders disrupting fundamental processes of socialization, communication and learning, collectively known as pervasive developmental disorders. This group of conditions is among the most common developmental disorders, affecting 1 in every 200 or so individuals. They are also the most strongly genetically related among developmental disorders, with recurrence risks within sibships of the order of 2 to 15% if a broader definition of affectedness is adopted. Their early onset, symptom profile, and chronicity implicate fundamental biological mechanisms involved in social adaptation. Advances in their understanding are leading to a new social neuroscience perspective of normative socialization processes and specific disruptions thereof. These processes may lead to the emergence of the highly heterogeneous phenotypes associated with autism, the paradigmatic pervasive developmental disorder, and its variants. This overview focuses on the history, nosology, and the clinical and associated features of the two most well-known pervasive developmental disorders - autism and Asperger syndrome.