Quartodecimanism ("fourteenism") was the practice of fixing the date of Pesach (Easter) to the 14th day of Nisan in the Jewish Calendar. It was one of several methods of fixing the date of the Pesach holiday. Quartodecimism was popular among Christians in Asia Minor and it is generally believed that this was the method specifically preferred by the followers of the Apostle John, since it was advocated by St Polycarp, a student of the Apostle.

In the second century AD a dispute arose over the churches of the East in Asia Minor and those of the West. The churches of the East celebrated Easter on the 14th of Nisan, but those of the West celebrated on the first day of the week, which was on Sunday(and of supposedly pagan origin, as some alleged, due to its simlarities to Ishtar). This differences resulted in the Apostolic Father Polycarp visiting Rome to settle the matter with Pope Anicetus. It was agreed that both should not interfere in how they celebrate Easter. However Anicetus' successor Pope Victor I later excommunicated the Quatodecimans for not adhering to the Easter practices of Rome thereby alienating them.

Despite this schism, the Quartodecimans Melito of Sardis and Polycarp, for example, are both recognized as Saints by both the Roman Catholic and Eastern Orthodox Churches. In 325CE, the First Council of Nicaea came to a decision that the Church as a whole should use a unified system, which was the Roman one.