The ability to attribute mental states such as beliefs, intentions, desires, and emotions to self and others, and to understand that others' mental states can be different from own mental states is called theory of mind or TOM. Others' behavior will be significant and understandable on the basis of development of this cognitive capacity. The basic element in theory of mind is perceiving intentionality of behavior and directedness of others' perception. The evolutionary origin of theory of mind is traced to primates. Theory of mind is probably an adaptive reaction to early social interactions (premack & Woodruff, 1978). In three last decades, many researches was conducted on the theory of mind development in normal children, neurophysiology of theory of mind in the brain and discovering involving regions in this cognitive action, the role of mirror neurons, and theoretical approaches. After broad investigations on the normal development of theory of mind, now psychopathology of TOM became centre of attention in disorders such as schizophrenia, personality disorders, autism spectrum disorders, Asperger syndrome, and so on. In this paper, history of TOM, theory of mind as an adaptive behavior in response to complexity of social life, theoretical approaches, stages of Tom development in intact children, cortical mechanisms of TOM, relationship between TOM and other cognitive abilities are discussed.