The Democratic Unionist Party (DUP) is the larger of the two main unionist political parties in Northern Ireland. Led by Ian Paisley, it is the largest party in Northern Ireland and the fourth-largest party in the British House of Commons. The DUP has strong links to Protestant churches, particularly the Free Presbyterian Church of Ulster; the church Ian Paisley founded, and is considered a Protestant political party. The party's youth wing is the Democratic Unionist Association (DUA).

Following on from the St Andrews Agreement in October 2006, the DUP has agreed with the Irish republican party Sinn Féin to enter into power-sharing devolved government in Northern Ireland. In the aftermath of the agreement there were reports of divisions within the DUP. Many of its leading members, including Members of Parliament (MPs) Nigel Dodds, David Simpson and Gregory Campbell were claimed to be in opposition to Paisley. All the party's MPs fully signed up to the manifesto for the 2007 Assembly elections, supporting power sharing in principle. An overwhelming majority of the party executive voted in favour of restoring devolution in a meeting in March 2007 ; however, the DUP's sole Member of the European Parliament (MEP), Jim Allister , and seven DUP councillors later resigned from the party in opposition to its plans to share power with Sinn Féin. They founded the Traditional Unionist Voice on 2007-12-07.