The Church of Scotland is the established church in Scotland, with roots in the 4th century Celtic Church of St Ninian, Whithorn, but current doctrine and organisation dating largely from radical reform by presbyterians, notably John Knox, since 1560. It is a Protestant and Reformed church, set in the tradition of John Calvin. Its doctrine is Trinitarian, and it accepts the Westminster Confession of Faith as its principal subordinate standard. Church government is Presbyterian, and exercised through a series of courts, from Kirk Sessions at the local level, through Presbyteries, Synods and ultimately, the General Assembly, which meets annually in Edinburgh. This system was initiated by John Knox in the First Book of Discipline, modified and refined by Andrew Melville in the Second Book of Discipline and ratified by Government in the Act of 1592.
Conflict between Episcopalians and Presbyterians prevailed in the seventeenth century, finally resolved by constitutional change in 1690, which confirmed the Presbyterian church as the Established Church of Scotland. The Episcopal Church in Scotland has been a non-established independent church since that time.
During the eighteenth and nineteenth centuries the unity of the Church of Scotland was broken by internal unrest and the breakaway of several new Presbyterian churches, most notably the Secession Church in 1733, and the Free Church of Scotland and the United Presbyterian Church of Scotland at the Disruption of 1843. In 1900 the Free Church and the United Presbyterian Church united to form the United Free Church of Scotland; and in 1929 their re-union with the Church of Scotland was effected. Some congregations abstained from the unions of 1900 and 1929, and these remain as independent Presbyterian denominations (principally the Free Church of Scotland; United Free Church of Scotland; Free Presbyterian Church of Scotland; Associated Presbyterian Churches; and Reformed Presbyterians). In 1990, there were 12 Synods, 49 Presbyteries, and 1685 Kirk Sessions in the Church of Scotland.