On Aggression (German: Das sogenannte Böse. Zur Naturgeschichte der Aggression, "So-called Evil: on the natural history of aggression") is a 1963 book by the ethologist Konrad Lorenz; it was translated into English in 1966.[1] As he writes in the prologue, "the subject of this book is aggression, that is to say the fighting instinct in beast and man which is directed against members of the same species." (Page 3)

The book was reviewed many times, both positively and negatively, by biologists, anthropologists, psychoanalysts and others. Much criticism was directed at Lorenz's extension of his findings on non-human animals to humans.