Petén is a department of the nation of Guatemala. It is geographically the most northern department of Guatemala. It is also the largest in size — at 12,960 square miles (33,600 km2). It is about one third of Guatemala's area. The capital is Flores. The population in 2005 was about 450,000.

The Petén department was formed by the Guatemalan government on 8 May 1866.