Door displaying the Ninety-five Theses at All Saints' Church, Wittenberg. According to popular account, Martin Luther nailed his Theses to this door, beginning the Reformation.

Protestantism is the second largest form of Christianity with collectively between 800 million and more than 900 million adherents worldwide or nearly 40% of all Christians.[1][2][a] It originated with the 16th century Reformation,[b] a movement against what its followers perceived to be errors in the Roman Catholic Church.[4] Protestants reject the Roman Catholic doctrine of papal supremacy and sacraments, but disagree among themselves regarding the real presence of Christ in the Eucharist.[5] They emphasize the priesthood of all believers, justification by faith alone (sola fide) rather than also by good works, and the highest authority of the Bible alone (rather than also with sacred tradition) in faith and morals (sola scriptura).[6] The "five solae" summarise basic theological differences in opposition to the Roman Catholic Church.[7]

Protestantism is popularly considered to have begun in Germany[c] in 1517 when Martin Luther published his Ninety-five Theses as a reaction against abuses in the sale of indulgences by the Roman Catholic Church, which purported to offer the remission of the temporal punishment of sins to their purchasers.[8] However, the term derives from the letter of protestation from German Lutheran princes in 1529 against an edict of the Diet of Speyer condemning the teachings of Martin Luther as heretical.[9] Although there were earlier breaks and attempts to reform the Roman Catholic Church—notably by Peter Waldo, John Wycliffe, and Jan Hus—only Luther succeeded in sparking a wider, lasting, and modern movement.[10] In the 16th century, Lutheranism spread from Germany[d] into Denmark, Norway, Sweden, Finland, Latvia, Estonia, and Iceland.[11] Reformed (or Calvinist) denominations spread in Germany,[e] Hungary, the Netherlands, Scotland, Switzerland and France by reformers such as John Calvin, Huldrych Zwingli, and John Knox.[12] The political separation of the Church of England from the pope under King Henry VIII began Anglicanism, bringing England and Wales into this broad Reformation movement.[f]

Protestants have developed