This paper discusses how the understanding of autism has changed in the 60 years since Leo Kanner first described the syndrome. Originally identified as an emotional disorder caused by parental ambivalence and rejection, autism today is universally seen as a neurobiological difficulty, whose cause is organic and related to atypical brain development. Evidence for the organic and genetic causes is presented, along with a discussion of how the understanding of autism has evolved during the past half century. The current understanding of autism as a developmental disorder has dramatically improved the quality of care and effectiveness of interventions for these youngsters and their families.