The ‘theory of mind’ deficit account explains social and communication problems in autism as resulting from difficulty tracking others’ thoughts. In this article I briefly describe the nature, history and implications of this influential account. The notion that people with autism show a sort of ‘mindblindness’ refined our understanding of their social-communicative symptoms, allowed neuroimaging investigation of the brain basis of social difficulties in autism, led to new attempts at intervention and highlighted areas of social cognition not impaired in this group.