The patriarch is the title of the head of certain of the ancient and self-governing churches of the East, and it marks the summit of the episcopal order in those churches.
Primacy among bishops
A patriarch is a bishop who holds the highest rank and jurisdiction within one of the historic patriarchal churches, presiding over its bishops and its affairs, and the title belonged historically to the bishops of the great sees of the early church, Rome, Constantinople, Alexandria, Antioch and Jerusalem, to which others were later added. The office is one of rank and jurisdiction built upon the order of bishop rather than a higher ordination, so the patriarch is a bishop first, raised to the presidency of his church.
Autocephaly and honour
In the Eastern Orthodox communion the patriarchs head the self-governing churches, and the Patriarch of Constantinople holds a primacy of honour as first among equals, without the universal jurisdiction claimed by the Bishop of Rome, so the office expresses a conception of church authority as a communion of self-governing churches rather than a single monarchy, which is at the heart of the difference between Orthodoxy and Rome. The Oriental Orthodox and the Eastern Catholic churches also have their patriarchs. Entry to the office is by election within the church concerned. The patriarch thus represents the head of an ancient and self-governing church, the senior bishop who presides over it, and the office embodies the Eastern understanding of a church led by a college of such heads in communion rather than by one supreme pontiff.