Lutheranism or Evangelical Lutheranism is a major branch of Protestantism that arose under the work of Martin Luther, the 16th-century German friar and reformer whose efforts to reform the theology and practices of the Catholic Church helped launch the Reformation in 1517. The Lutheran churches adhere to the Bible and the ecumenical creeds, with Lutheran doctrine being explicated in the Book of Concord. Lutherans hold themselves to be in continuity with the apostolic church and affirm the writings of the Church Fathers and the first four ecumenical councils.