In this review the specific language and communication impairments of autistic individuals are discussed and contrasted with non-specific impairments. All the impairments that are unique to autism concern the use of language for the purpose of intentional (but not instrumental) communication. The specific communication failure can be identified with a limitation in the computing of relevance and as a lack of taking account of mental states. This is a consequence of a subtle, but far-reaching, cognitive dysfunction. The dysfunction is likely to involve the formation and use of second-order representations. The same problem also leads to specific impairment in social relationships and imaginative play.