Calvinism (also called the Reformed tradition, Reformed Christianity, Reformed Protestantism, or the Reformed faith) is a major branch of Protestantism that follows the theological tradition and forms of Christian practice of John Calvin and other Reformation-era theologians.
Calvinists broke from the Roman Catholic Church in the 16th century. Calvinists differ from Lutherans on the real presence of Christ in the Eucharist, theories of worship, and the use of God's law for believers, among other things. As declared in the Westminster and Second Helvetic confessions, the core doctrines are predestination and election. The term Calvinism can be misleading, because the religious tradition which it denotes has always been diverse, with a wide range of influences rather than a single founder. In the context of the Reformation, Huldrych Zwingli began the Reformed tradition in 1519 in the city of Zürich. His followers were instantly deemed Zwinglians, consistent with the Catholic practice of naming heresy after its founder. Very soon, Zwingli was joined by Martin Bucer, Wolfgang Capito, William Farel, Johannes Oecolampadius and other early Reformed thinkers. The namesake of the movement, French reformer John Calvin, converted to the Reformed tradition from Roman Catholicism only in the late 1520s or early 1530s as it was already being developed. The movement was first called Calvinism, referring to John Calvin, by Lutherans who opposed it. Many within the tradition find it either an indescriptive or an inappropriate term and would prefer the word Reformed to be used instead.
The most important Reformed theologians include Huldrych Zwingli, John Calvin, Martin Bucer, William Farel, Heinrich Bullinger, Peter Martyr Vermigli, Theodore Beza, and John Knox. In the twentieth century, Abraham Kuyper, Herman Bavinck, B. B. Warfield, J. Gresham Machen, Karl Barth, Martyn Lloyd-Jones, Cornelius Van Til, and Gordon Clark were influential. Contemporary Reformed theologians include J. I. Packer, John MacArthur, R. C. Sproul, Timothy J. Keller, John Piper, David Wells, and Michael Horton.
Reformed churches may exercise several forms of ecclesiastical polity; most are presbyterian or congregationalist, though some are episcopalian. Calvinism is largely represented by Continental Reformed, Presbyterian, and Congregationalist traditions. The biggest Reformed association is the World Communion of Reformed Churches with more than 100 million members in 211 member denominations around the world. There are more conservative Reformed federations such as the World Reformed Fellowship and the International Conference of Reformed Churches, as well as independent churches.