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. It originated with the 16th century Reformation, a movement against what its followers perceived to be errors in the Roman Catholic Church. Protestants reject the Roman Catholic doctrine of papal supremacy and sacraments, but disagree among themselves regarding the real presence of Christ in the Eucharist. 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). The "five solae" summarise basic theological differences in opposition to the Roman Catholic Church.
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.
The belief, emphasized by Luther, in the Bible as the highest source of authority for the church. The early churches of the Reformation believed in a critical, yet serious, reading of scripture and holding the Bible as a source of authority higher than that of church tradition. The many abuses that had occurred in the Western Church before the Protestant Reformation led the Reformers to reject much of its tradition, though some would maintain tradition has been maintained and reorganized in the liturgy and in the confessions of the Protestant churches of the Reformation. In the early 20th century, a less critical reading of the Bible developed in the United States, leading to a "fundamentalist" reading of Scripture. Christian fundamentalists read the Bible as the "inerrant, infallible" Word of God, as do the Roman Catholic, Eastern Orthodox, Anglican and Lutheran churches, but interpret it in a literalist fashion without using the historical critical method.
Movements emerging around the time of the Protestant Reformation, but not a part of Protestantism, e.g. Unitarianism also reject the Trinity. This often serves as a reason for exclusion of the Stone-Campbell Restoration Movement, Unitarian Universalism, Oneness Pentecostalism and other movements from Protestantism by various observers. Unitarianism continues to have a presence mainly in Transylvania, England and the United States, as well as elsewhere.
The Protestant movement began to diverge into several distinct branches in the mid-to-late 16th century. One of the central points of divergence was controversy over the Eucharist. Early Protestants rejected the Roman Catholic dogma of transubstantiation, which teaches that the bread and wine used in the sacrificial rite of the Mass lose their natural substance by being transformed into the body, blood, soul, and divinity of Christ. They disagreed with one another concerning the presence of Christ and his body and blood in Holy Communion.
Later on, theological disputes caused a split within the Hussite movement. Utraquists maintained that both the bread and the wine should be administered to the people during the Eucharist. Another major faction were the Taborites, who opposed the Utraquists in the Battle of Lipany during the Hussite Wars. There were two separate parties among the Hussites: moderate and radical movements. Other smaller regional Hussite branches in Bohemia included Adamites, Orebites, Orphans and Praguers.
The Reformation was a triumph of literacy and the new printing press invented by Johannes Gutenberg. Luther's translation of the Bible into German was a decisive moment in the spread of literacy, and stimulated as well the printing and distribution of religious books and pamphlets. From 1517 onward, religious pamphlets flooded much of Europe.
Parallel to events in Germany, a movement began in Switzerland under the leadership of Huldrych Zwingli. Zwingli was a scholar and preacher, who in 1518 moved to Zurich. Although the two movements agreed on many issues of theology, some unresolved differences kept them separate. A long-standing resentment between the German states and the Swiss Confederation led to heated debate over how much Zwingli owed his ideas to Lutheranism. The German Prince Philip of Hesse saw potential in creating an alliance between Zwingli and Luther. A meeting was held in his castle in 1529, now known as the Colloquy of Marburg, which has become infamous for its failure. The two men could not come to any agreement due to their disputation over one key doctrine.
The Scottish Reformation of 1560 decisively shaped the Church of Scotland. The Reformation in Scotland culminated ecclesiastically in the establishment of a church along Reformed lines, and politically in the triumph of English influence over that of France. John Knox is regarded as the leader of the Scottish Reformation. The Scottish Reformation Parliament of 1560 repudiated the pope's authority by the Papal Jurisdiction Act 1560, forbade the celebration of the Mass and approved a Protestant Confession of Faith. It was made possible by a revolution against French hegemony under the regime of the regent Mary of Guise, who had governed Scotland in the name of her absent daughter.
The Second Great Awakening began around 1790. It gained momentum by 1800. After 1820, membership rose rapidly among Baptist and Methodist congregations, whose preachers led the movement. It was past its peak by the late 1840s. It has been described as a reaction against skepticism, deism, and rationalism, although why those forces became pressing enough at the time to spark revivals is not fully understood. It enrolled millions of new members in existing evangelical denominations and led to the formation of new denominations.
Perhaps the oldest official united church is found in Germany, where the Evangelical Church in Germany is a federation of Lutheran, United (Prussian Union) and Reformed churches, a union dating back to 1817. The first of the series of unions was at a synod in Idstein to form the Protestant Church in Hesse and Nassau in August 1817, commemorated in naming the church of Idstein Unionskirche one hundred years later.