Studies of twins have been used to highlight the contribution of genetic and environmental causes of behavior as monozygotic twins (MZ) share 100% of their genes. For autism spectrum disorders (ASD), the rate of concordance for MZ twins has been estimated between 60-90%, suggesting a strong contribution of genetic factors toward the disease. The proposed study aims to explore possible neurocognitive and neurophysiological endophenotypes of three domains that contribute to autism: social processing, language, and executive functioning in MZ twin pairs concordant for autism. In a sample of concordant twin pairs (either with ASD or typical development) behavioral and electrophysiological indices of social processing (face memory, imitation ability, face processing related ERP components and imitation related EEG components); language (phonological processing ability, pragmatics, verbal IQ, phonological processing related ERP mismatch negativity); and executive functioning (inhibition, spatial working memory, set shifting, inhibition related ERP components) will be examined. This project will address the concordant trait components of the autism phenotype and may accelerate the discovery of specific common genetic and neurobiologic causes of autism. Additionally, the proposed project will directly test assumptions that behavioral and electrophysiological measures can be used to assess endophenotypes in autism and how concordance rates may be altered by the behavioral profile found in autism.