A Fraternal order of protestants, mostly peculiar to Northern Ireland, but with members dispersed around the Republic of Ireland, the United Kingdom and elsewhere. Their name is drawn from William of Orange (or King Billy), who defeated the Catholic King James at the Battle of the Boyne in 1690. The structure of the organisation is similar to that of the Freemasons, although the two groups are not related.

Orangemen describe their organisation as a religious society, but religion and politics are not easily separated in Northern Ireland. They are associated with Protestant hegemony in the province, and are therefore not popular with republicans. Most Catholics and nationalists simply do not understand them, and the order does not go out of its way to popularise itself beyond its own constituency. Their beliefs are summed up in the Basis of the Orange Institution.

Orangeism expresses itself most visibly during the "Marching Season", when Orangemen parade through the streets in various parts of the province (as well as in Co. Donegal), wearing their traditional sashes and collarettes. These marches are often accompanied by "Blood-and-Thunder" marching bands, and supporters from outside the order. These marches have led to a great deal of contention in recent years, especially when the route passes through a predominantly Catholic area. The routes of the parades, however, are fiercely defended by the Order as traditional, and in many cases they have refused to entertain the prospect of engaging in talks with the local residents. This has led to massive trouble at certain flashpoints, most famously Drumcree in Portadown.