In Capgras syndrome, the patient feels that a person familiar to him , usually a family member has been replaced by a double i.e. an identical looking imposter. Capgras Syndrome and Fregoli syndrome along with some other conditions are classified as delusional misidentification syndrome.

It is named after Joseph Capgras (1873-1950), a French psychiatrist who first described the disorder in a paper by Capgras and Reboul-Lachaux in 1923. They used the term l'illusion des sosies (the illusion of doubles) to describe the case of a French woman who complained that various doubles had taken the place of people she knew. However, the term illusion has a subtly different meaning from delusion in psychiatry so Capgras delusion is used as a more suitable name.