Protestantism is a branch of Christianity that follows the theological tenets of the Protestant Reformation, a movement that began in the 16th century with the goal of reforming the Catholic Church from perceived errors, abuses, and discrepancies.
Protestantism emphasizes the Christian believer's justification by God in faith alone (sola fide) rather than by a combination of faith with good works as in Catholicism; the teaching that salvation comes by divine grace or "unmerited favor" only (sola gratia); the priesthood of all believers in the Church; and the sola scriptura ("scripture alone") that posits the Bible as the sole infallible source of authority for Christian faith and practice. Protestants reject the Catholic doctrine of papal supremacy, and have variant views on the number of sacraments, the real presence of Christ in the Eucharist, and matters of ecclesiastical polity and apostolic succession. Other Protestant denominations and non-denominational Protestants may be typically unconcerned about most of these theological issues and focus only on their perception of explicit Christian teachings in the Bible itself. The five solae of Lutheran and Reformed Christianity summarize basic theological differences in opposition to the Catholic Church. Today, it is the second-largest form of Christianity, with a total of 800 million to 1 billion adherents worldwide or about 37% of all Christians.
The Reformation began in the Holy Roman Empire in 1517, when Martin Luther published his Ninety-five Theses as a reaction against abuses in the sale of indulgences by the Catholic Church, which purported to offer the remission of the temporal punishment of sins to their purchasers. The term, however, 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.
In the 16th century, Lutheranism spread from Germany into Denmark, Norway, Sweden, Finland, Latvia, Estonia, and Iceland.