Human adults conceive of one another as beings with minds, and attribute to one another mental states like perceptions, desires and beliefs. That is, we understand other people using a 'Theory of Mind'. The current study investigated the contributions of four brain regions to Theory of Mind reasoning. The right temporo-parietal junction (RTPJ) was recruited selectively for the attribution of mental states, and not for other socially relevant facts about a person, and the response of the RTPJ was modulated by the congruence or incongruence of multiple relevant facts about the target's mind. None of the other three brain regions commonly implicated in Theory of Mind reasoning--the left temporo-parietal junction (LTPJ), posterior cingulate (PC) and medial prefrontal cortex (MPFC)--showed an equally selective profile of response. The implications of these results for an alternative theory of reasoning about other minds--Simulation Theory--are discussed.