In the German Advent wreath tradition, four candles are typically lit one by one on the four Sundays before Christmas.
The Advent wreath is a ring of evergreen branches carrying four candles. One candle is lit on the first Sunday of Advent, with another added on each following Sunday. By the fourth Sunday, all four candles are burning.
The custom is widely credited to Johann Hinrich Wichern, a German Lutheran pastor and educator. In 1839, he used a large wooden wheel with candles at a mission school in Hamburg to help children count the days until Christmas. The later familiar wreath normally used four Sunday candles.
Advent does not always begin on the same calendar date because Christmas Day is fixed on December 25, while the Sundays before it shift from year to year. Some wreaths also include a fifth candle for Christmas Day, but that is not one of the four standard Advent Sunday candles.