Pentarchy (from Greek pente, five, and arche, rule) is a term in the history of Christianity for the idea of universal rule over all of Christendom by the heads (or Patriarchs) of the five major episcopal sees of the Roman Empire: Rome, Constantinople, Alexandria, Antioch, and Jerusalem. The idea came about due to the political and ecclesiastical prominence of these five sees, but the concept of their universal and exclusive authority was firmly tied to the administrative structure of the Roman Empire. The idea of the pentarchy was first tangibly expressed in the laws of Emperor Justinian I (527–565), particularly in Novella 131. The Quinisext Council of 692 gave it formal recognition and ranked the sees in order of preeminence. Especially following Quinisext, the pentarchy was at least philosophically accepted in Eastern Christianity, but generally not in the West, which rejected the Council.

The greater authority of these sees in relation to others was tied to their political and ecclesiastical prominence; all were located in important cities and regions of the Roman Empire and were important centers of the Church. Rome, Alexandria and Antioch were prominent from the time of early Christianity, while Constantinople came to the fore upon becoming the imperial residence in the 4th century. Thereafter it was ranked consistently just after Rome. Jerusalem received a ceremonial place due to the city's importance in the early days of Christianity. Justinian and the Quinisext Council excluded from their pentarchical arrangement churches outside the Empire, such as the then-flourishing Church of the East in Sassanid Persia, which they saw as heretical. Within the empire they recognized only the Chalcedonian incumbents, regarding as illegitimate the non-Chalcedonian claimants of Alexandria and Antioch.