This document discusses autism spectrum disorder (ASD) and Asperger's syndrome. It notes that ASD is characterized by impaired social interaction and communication as well as repetitive behaviors. Asperger's is distinguished by less severe impairment overall and no significant language delay, though language usage is still atypical and social skills lacking. The distinction between Asperger's and autism may be removed in future diagnostic manuals. Causes are unclear but likely involve genetic, brain, and environmental factors interacting.