The Presbyterian Church is a mainline Protestant denomination founded during the Reformation of the 1500s. Presbyterians and the Reformed churches were differentiated from the Lutherans over the sacraments and church government, among other doctrines. John Knox founded the Scottish Presbyterian church in about 1560. Presbyterianism can thus be seen as Calvinism in the Scottish tradition.
Traditionally, the ethics of the church lean towards strictness and firm church- and self-discipline. Authority in Presbyterian churches is given to Scripture. Presbyterians are Calvinist in doctrine, and their faith is summarized in the Westminster Standards. Church organization is highly structured with a representational system of ministers and laypersons (presbyters) in local, regional and national bodies (called presbyteries and synods'). The largest governing body of the Presbyterian Church (U.S.A.) is called the General Assembly and is made up of representatives of all the presbyteries.
Presbyterianism is the dominant and official religion in Scotland. Because of this, it was historically strong in areas of the United States where large numbers of Scots and Scots-Irish settled. Many of these, however, would later convert to the Baptist and Methodist faiths during the early 1800s.
In the early 20th century, the predecessor to the Presbyterian Church (U.S.A.), which represented a majority of American Presbyterians, modified much of its theology. In reaction to such moves towards Liberal Christianity, the well-respected scholar J. Gresham Machen was forced out of Princeton Theological Seminary and the main Presbyterian Church. He then helped to found Westminster Theological Seminary and the Orthodox Presbyterian Church.
More recently, another such split-off occurred and produced the Presbyterian Church in America. Its membership is substantially greater than that of the Orthodox Presbyterian Church, making the PCA the leader among the various conservative Presbyterian bodies in the United States.