See Eilenberg and Mac Lane, Ann Math 1954.
Bourbaki talk by Pirashvili around 1999: review
Book: Franjou, Vincent(F-NANTC-LM); Friedlander, Eric M.(1-NW); Pirashvili, Teimuraz(GE-AOS); Schwartz, Lionel(F-PARIS13-GA). Rational representations, the Steenrod algebra and functor homology. Panoramas et Synthèses 16. Société Mathématique de France, Paris, 2003. xxii+132 pp. ISBN: 2-85629-159-7.
Pirashvili and Franjou: Strict polynomial functors and coherent functors.
Gambino and Kock on polynomial functors and polynomial monads http://arxiv.org/abs/0906.4931
nLab page on Polynomial functor