Gimbutas, Marija. The Goddesses and Gods of Old Europe: 6500-3500 BC: Myths and Cult Images. London: Thames and Hudson, 1982. Print.

Hankoff, Leon D. “Why Are the Healing Gods Twins?” Yale Journal of Biology and Medicine 50 (1977): 307-19. Web. 18 June 2014.

Leeming, David Adams. From Olympus to Camelot: The World of European Mythology. Oxford: Oxford UP, 2003. Print.

Lincoln, Bruce. “The Indo-European Cattle-Raiding Myth.” History of Religions 16.1 (1976): 42-65. JSTOR. Web. 19 June 2014. <http://www.jstor.org/stable/10.2307/1062296?ref=search-gateway:adf083d99a2468803ff19ae81c97a563>.

Puhvel, Jaan. Comparative Mythology. Baltimore: Johns Hopkins UP, 1987. Print.

Winn, Shan M. M. Heaven, Heroes, and Happiness: The Indo-European Roots of Western Ideology. Lanham: U of America, 1995. Print.

Littleton, C. Scott. The New Comparative Mythology: An Anthropological Assessment of the Theories of Georges Dumézil. Berkeley: U of California, 1973. Print.

Eliade, Mircea. Patterns in Comparative Religion. Cleveland: World, 1963. Print.