Presbyterianism is Reformed in doctrine and shares that doctrine with Continental Reformed and Congregational churches. What makes it a distinct tradition is a claim about church government, and Presbyterians have historically held that claim as a matter of divine right rather than convenience.
The word comes from the Greek for elder. In Presbyterian order the church is governed neither by bishops nor by the independent congregation but by elders sitting in courts. The local congregation is ruled by a session of elected ruling elders with the minister, who is a teaching elder, as moderator. Above it sits the presbytery, which is the crucial body: it, not the congregation, ordains ministers, and it holds authority over them and over the congregations in its bounds. Above that sit synod and general assembly.
Two features follow. Ministers and elders are equal in the courts, there is no order above presbyter, and every decision can be appealed upward, which makes Presbyterianism the most legally minded of the Protestant traditions. Its disputes are conducted through overtures, judicial commissions and points of order, and its history is largely a history of constitutional argument.
The tradition dates from the Scottish Reformation of 1560 under John Knox, who had been in Geneva, and its distinctive instruments are the Book of Discipline, which set out the polity, and later the Westminster Confession of 1646 with its two catechisms, produced by an English assembly during the civil war and adopted in Scotland. The Westminster Standards remain the doctrinal reference of Presbyterian churches worldwide, though the terms on which ministers subscribe them, fully, or as containing the system of doctrine, or more loosely still, differ sharply from body to body and are themselves a recurring source of division.