anniversary of the day Martin Luther is said to have posted his Ninety-five Theses on the door of the Castle Church in Wittenberg, Ger. (Oct. 31, 1517), later identified by Protestants as the beginning of the Reformation. (See Researcher's Note.) The European Lutheran territorial churches at first commemorated the Reformation on various days, among them the anniversary of Luther's birth (November 10), his death (February 18), and presentation of the Augsburg Confession (June 25). The centennial celebrations of 1617 focussed attention on October 31; in the sesquicentennial year (1667) Elector John George II decreed this date as annual Reformation Day in Saxony. German Lutheran and Union territorial churches have come gradually to follow this example and specify October 31 or the Sunday following (or preceding).

Among English-speaking Lutherans, the churches that use the Lutheran Liturgy (1948) keep October 31 as Reformation Day; those using the Service Book and Hymnal (1958) observe October 31 as Reformation Day and may keep the preceding Sunday as Reformation Sunday. The liturgical colour is red. Many churches in the Reformed and the Evangelical traditions also mark the day, often with special services focussed on the Reformation and its effects.