Reformation Day is a religious holiday celebrated in remembrance of the Reformation, particularly by Lutheran communities. In the United States churches often transfer the holiday, so that it falls on the Sunday on or before October 31.
Eating reformation buns
Legal holiday in:
Parts of Germany (Brandenburg, Mecklenburg-Vorpommern, Saxony, Saxony-Anhalt and Thuringia), Slovenia, Chile
John George II, Elector of Saxony
Martin Luther is said to have nailed his 95 Theses to the door of the Schlosskirche (castle church) in Wittenberg on the 31st of October 1517, sparking the Reformation.