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.
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 it viewed as 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.
— John Calvin, Leçons ou commentaires et expositions sur les Revelations du prophete Jeremie, 1565
Despite its negative connotation, this designation became increasingly popular in order to distinguish Calvinists from Lutherans and from newer Protestant branches that emerged later. The vast majority of churches that trace their history back to Calvin (including Presbyterians, Congregationalists, and a row of other Calvinist churches) do not use it themselves, since the designation "Reformed" is more generally accepted and preferred, especially in the English-speaking world. Moreover, these churches claim to be—in accordance with John Calvin's own words—"renewed accordingly with the true order of gospel".
Since the Arminian controversy, the Reformed tradition—as a branch of Protestantism distinguished from Lutheranism—divided into two separate groups: Arminians and Calvinists. However, it is now rare to call Arminians a part of the Reformed tradition. While the Reformed theological tradition addresses all of the traditional topics of Christian theology, the word Calvinism is sometimes used to refer to particular Calvinist views on soteriology and predestination, which are summarized in part by the Five Points of Calvinism. Some have also argued that Calvinism as a whole stresses the sovereignty or rule of God in all things including salvation.