Communication deficits are a core symptom or ASD, and the assessment of individuals with these disorders requires both formal testing and careful observation of natural and seminatural communicative activities. For children in prelinguistic phases of communication, assessment is aimed at establishing the communicative basis for a formal language system and looking at the frequency, range, and means of expression of communicative acts. Children in the early stages of language use will need to be assessed not only in terms of their vocabularies and sentence structures, but with regard to the unusual communicative patterns that often accompany ASD, such as echolalia, pronoun errors, and significant deficits in pragmatics and receptive language. Some children at this level may require evaluation to determine the best alternative mode of communication if speech has not yet emerged, and an augmentative and alternative communication (AAC) system should be considered. For individuals at advanced language levels, assessment will focus on social uses of communication (particularly pragmatic, narrative, and prosodic skills), and may include an assessment of their written language. For people at all developmental levels and at all points along the autistic spectrum, a comprehensive evaluation of strengths and needs in the area of communication is essential to the development of an effective plan for improving communicative competence.