In the 16th century, Martin Luther, Huldrych Zwingli, and John Calvin inaugurated what has come to be called Protestantism. Luther's primary theological heirs are known as Lutherans. Zwingli and Calvin's heirs are far broader denominationally, and are broadly referred to as the Reformed Tradition. Most Protestant traditions branch out from the Reformed tradition in some way. In addition to the Lutheran and Reformed branches of the Reformation, there is Anglicanism after the English Reformation. The Anabaptist tradition was largely ostracized by the other Protestant parties at the time, but has achieved a measure of affirmation in more recent history. Some but not most Baptists prefer not to be called Protestants, claiming a direct ancestral line going back to the apostles in the 1st century.
The oldest Protestant groups separated from the Catholic Church in the 16th century Protestant Reformation, followed in many cases by further divisions. For example, the Methodist Church grew out of Anglican minister John Wesley's evangelical and revival movement in the Anglican Church. Several Pentecostal and non-denominational Churches, which emphasize the cleansing power of the Holy Spirit, in turn grew out of the Methodist Church. Because Methodists, Pentecostals, and other evangelicals stress "accepting Jesus as your personal Lord and Savior", which comes from Wesley's emphasis of the New Birth, they often refer to themselves as being born-again. Estimates of the total number of Protestants are very uncertain, partly because of the difficulty in determining which denominations should be placed in these categories, but it seems clear that Protestantism is the second largest major group of Christians after Catholicism in number of followers (although the Orthodox Church is larger than any single Protestant denomination). Often that number is put at 800 million. Protestantism, along with the Orthodox Church (appx. 200 million) and the Catholic Church (appx. 1.1 billion) form a total of 2.1 billion Christianity followers. A special grouping are the Anglican churches descended from the Church of England and organised in the Anglican Communion. Some Anglican churches consider themselves both Protestant and Catholic. Some Anglicans consider their church a branch of the "One Holy Catholic Church" alongside of the Roman Catholic and Eastern Orthodox Churches, a concept rejected by the Roman Catholic Church and some Eastern Orthodox. Some groups of individuals who hold basic Protestant tenets identify themselves simply as "Christians" or "born-again Christians". They typically distance themselves from the confessionalism and/or creedalism of other Christian communities by calling themselves "non-denominational". Often founded by individual pastors, they have little affiliation with historic denominations.