Polycrates of Ephesus was a second-century Christian bishop who served the church in Ephesus during the Roman era. Belonging to a prominent religious family, he was the eighth relative to hold the office of bishop in his community. He is primarily recognized for his leadership during the Quartodeciman controversy, where he defended the tradition of celebrating Easter on the fourteenth day of Nisan. To support this practice, he convened a synod and wrote a significant letter to Pope Victor to maintain the customs handed down from the apostles.