For humans, as for many other species, the social world has provided an important niche for evolutionary adaptation; but more than any other species, we are able to leverage the social world because of our capacity to create, learn about, and take part in culture. One of the most powerful components of our capacity to leverage the social world is theory of mind, that is, the ability to understand the mental life of other people. More specifically, having a theory of mind is having an understanding that people have thoughts, perceptions, beliefs, desires, and other mental states that guide behavior. In this entry, key points in the history of the field are reviewed starting with the false belief test and the theory-of-mind impairment in autism; ...