Advent calendars typically don’t follow the full 4 week period of Advent. Instead, they begin on December 1 and mark the 24 days leading up to Christmas. Today, most Advent calendars include paper doors that open to reveal an image, Bible verse, or piece of chocolate. The tradition dates to the mid-19th century, when German Protestants made chalk marks on doors or lit candles to count the days leading up to Christmas.