N. J. Allen's main contributions to anthropology were in the fields of kinship theory, the history of anthropology, comparative Indo-European mythology, and the ethnography of eastern Nepal and the Tibetan cultural area. He is known for his theory of the origin of kinship in quadripartite structures. In Indo-European comparativism he is known for his reworking of Dumézil's three functions by the addition of a fourth sacred pole, which can have both positive and negative valences. Therefore, the key underlying structures, when comparing myths from different parts of the Indo-European world, may be either fourfold or fivefold.