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. The movement was first called Calvinism by Lutherans who opposed it referring to French reformer John Calvin, and many within the tradition would prefer to use the word Reformed.
Early influential Reformed theologians include Ulrich 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 80 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.
Calvinism is named after John Calvin. It was first used by a Lutheran theologian in 1552. It was a common practice of the Catholic Church to name what they perceived to be heresy after its founder. Nevertheless, the term first came out of Lutheran circles. Calvin denounced the designation himself:
They could attach us no greater insult than this word, Calvinism. It is not hard to guess where such a deadly hatred comes from that they hold against me.