The death instinct (Thanatos, or Death Drive) was defined by Sigmund Freud, in Jenseits des Lustprinzips (Beyond the Pleasure Principle) (1920; English translation 1922).

Freud begins the work considering the experience of trauma and traumatic events (particularly the trauma experienced by soldiers returning from World War I). The most curious feature of highly unpleasant experiences for Freud was that subjects often tended to repeat or re-enact them. This appeared to violate the "pleasure principle," the drive of an individual to maximize his or her pleasure. Freud found this repetition of unpleasant events in the most ordinary of cirumstances, even in children's play (such as the celebrated Fort/Da ("Here"/"Gone") game played by Freud's grandson). After hypothesizing a number of causes (particularly the idea that we repeat traumatic events in order to master them after the fact), Freud considered the existence of a fundamental death wish or death instinct, referring to an individual's own need to die. Organisms, according to this idea, were driven to return to a pre-organic, inanimate state—but they wished to do so in their own way.

In psychoanalytical theory, the death instinct (or death drive) opposes Eros. The "death instinct" signals a desire to give up the struggle of life and return to quiescence and the grave. This should not be confused with a similar urge/force destrudo.

Thanatos (psicoanalisi)