Polycrates of Ephesus (/pəˈlɪkrəˌtiːz/; Greek: Πολυκράτης; fl. c. 130 – 196) was an Early Christian bishop who resided in Ephesus.
Roberts and Donaldson noted that Polycrates "belonged to a family in which he was the eighth Christian bishop; and he presided over the church of Ephesus, in which the traditions of St. John were yet fresh in men's minds at the date of his birth. He had doubtless known Polycarp, and Irenaeus also. He seems to have presided over a synod of Asiatic bishops (A.D. 196) which came together to consider this matter of the Paschal feast. It is surely noteworthy that nobody doubted that it was kept by a Christian and Apostolic ordinance."
Polycrates is best known for his letter addressed to the Roman Bishop Victor who was attempting to find a consensus about the proper date to celebrate Easter, see also Quartodecimanism.
The Church historian Eusebius wrote,
Here is what Eusebius records that Polycrates wrote,
Pope Victor attempted to cut off from the common unity Polycrates and others for taking this stance, but later reversed his decision after Irenaeus and others interceded. It is unclear what happened to Polycrates after his letter.
Polycrates' letter has been used as proof against the argument that the Churches in Asia Minor accepted the authority of the bishops at Rome.