The term Tetrarchy (Greek: "leadership of four [people]") describes any system of government where power is divided among four individuals, but usually refers to the tetrarchy instituted by Roman Emperor Diocletian in 293, marking the end of the Crisis of the Third Century and the recovery of the Roman Empire.

This Tetrarchy lasts until c.313, when internecine conflict eliminates most of the claimants to power, leaving Constantine in the West and Licinius in the East.