Catholic Encyclopedia: Essenes
One of three leading Jewish sects mentioned by Josephus as flourishing in the second century B.C., the others being the Pharisees and the Sadducees. Concerning their origin, history, and tenets there has been much inconclusive controversy. The only ancient authorities we have are a few paragraphs in Philo Judeaeus, a somewhat lengthier description in Josephus, and a scanty notice in Pliny. The following synopsis is derived mainly from the first two.