The term "social cognition" generally refers to the mental operations that underlie social interactions including the perception and interpretation of the intentions, dispositions, and behaviors of others and the generation of a response to these behaviors. Social cognition has been considered a valuable and promising field that strives to understand the nature and outcome of major mental disorders. This article discusses the concept of social cognition and its relationship to Theory of Mind (ToM). Theory of Mind in autistic spectrum disorders has been studied since the 1980s, and cognitive impairments in these disorders may be restricted to ToM deficits because other cognitive domains and nonsocial intelligence are preserved. This article addresses the issues of human ontogeny, reviews the main findings from research on schizophrenia and bipolar disorder, and summarizes the tools commonly used in the assessment of these illnesses.