Protestantism is a form of Christianity that originated with the 16th-century Reformation,[lower-alpha 1] a movement against what its followers perceived to be errors in the Catholic Church.[1] Protestants originating in the Reformation reject the Roman Catholic doctrine of papal supremacy, but disagree among themselves regarding the number of sacraments, the real presence of Christ in the Eucharist, and matters of ecclesiastical polity and apostolic succession.[2][3] They emphasize the priesthood of all believers; justification by faith (sola fide) rather than by good works; the teaching that salvation comes by divine grace or "unmerited favor" only, not as something merited (sola gratia); and either affirm the Bible as being the sole highest authority (sola scriptura "scripture alone") or primary authority (prima scriptura "scripture first") for Christian doctrine, rather than being on parity with sacred tradition.[4][5] The five solae of Lutheran and Reformed Christianity summarise basic theological differences in opposition to the Catholic Church.[6][4]

Door displaying the Ninety-five Theses at All Saints' Church, Wittenberg. According to tradition, in 1517 Martin Luther nailed his Theses to this door, beginning the Reformation

Protestantism began in Germany[lower-alpha 2] 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.[7] 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.[8] Although there were earlier breaks and attempts to reform the Catholic Church, notably by Peter Waldo, John Wycliffe and Jan Hus, only Luther succeeded in sparking a wider, lasting and modern movement.[9] In the 16th century, Lutheranism spread from Germany[lower-alpha 3] into Denmark, Norway, Sweden, Finland, Latvia, Estonia and Iceland.[10] Calvinist churches spread in Germany,[lower-alpha 4] Hungary, the Netherlands, Scotland, Switzerland and France by Protestant Reformers such as John Calvin, Huldrych Zwingli and John Knox.[11] 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.[lower-alpha 5]

Today, Protestantism constitutes the second-largest form of Christianity (after Catholicism), with a total of 800 million to 1 billion adherents worldwide or about 37% of all Christians.[12][13][lower-alpha 6] Protestants have developed their own culture, with major contributions in education, the humanities and sciences, the political and social order, the economy and the arts and many other fields.[15] Protestantism is diverse, being more divided theologically and ecclesiastically than the Catholic Church, the Eastern Orthodox Church or Oriental Orthodoxy.[16] Without structural unity or central human authority,[16] Protestants developed the concept of an invisible church, in contrast to the Catholic, the Eastern Orthodox Church, the Oriental Orthodox Churches, the Assyrian Church of the East and the Ancient Church of the East, which all understand themselves as the one and only original church—the "one true church"—founded by Jesus Christ.[15] Some denominations do have a worldwide scope and distribution of membership, while others are confined to a single country.[16] A majority of Protestants[lower-alpha 7] are members of a handful of Protestant denominational families: Adventists, Anabaptists, Anglicans/Episcopalians, Baptists, Calvinist/Reformed,[lower-alpha 8] Lutherans, Methodists, and Pentecostals.[12] Nondenominational, Charismatic, Evangelical, Independent, and other churches are on the rise, and constitute a significant part of Protestantism.[18][19]