The Essenes was a Jewish religious sect that flourished from the 2nd century BCE to the 1st century CE. They were opposed to the Pharisees and Saducees. They are discussed in some detail by Josephus and Philo Judaeus. Many scholars believe that the community at Qumran that produced the Dead Sea Scrolls was an offshoot of the Essenes. A smaller number of scholars believe that the Dead Sea sect may be an offshoot of the Saducees.
Reference Lawrence H. Schiffman, "From Text to Tradition: A History of Second Temple & Rabbinic Judaism", Ktav Publishing House, 1991