This work gives a detailed account and a reappraisal of Edward Westermarck's thought. Westermarck had versatile relations to Victorian evolutionists (Wallace, Tylor, Spencer), and to British social anthropologists (Frazer, Haddon, Rivers, Malinowski) and psychologists (Shand, Sully). Westermarck was a pioneer of anthropological fieldwork, and his writings on the history of marriage and on the origin and development of moral ideas are modern classics. He was a transitional figure between evolutionism, on the one hand, and functionalism and structuralism, on the other hand. Westermarck's theories of exogamy and incest, and his notions of psychological ethics, moral emotions and concepts, and expanding morality were referred to by Durkheim and Freud, as they are referred to by present-day evolutionary theorists.