Northern Ireland (Tuaisceart Éireann, Ulster Scots: Norlin Airlann) is a constituent country of the United Kingdom, lying in the northeast of the island of Ireland, covering 5,459 square miles (14,139 km²), about a sixth of the island's total area. At the time of the UK Census in April 2001, its population was 1,685,000, between a quarter and a third of the island's total population.

Northern Ireland consists of six of the nine counties of the province of Ulster. In the UK, it is generally known as one of the four Home Nations that form the Kingdom. Some of these terms have controversial implications in relation to political ideologies concerning the constitutional status of Northern Ireland.

As an administrative division of the United Kingdom, Northern Ireland was defined by the Government of Ireland Act, 1920, and has had its own form of devolved government in a similar manner to Scotland and Wales. The Northern Ireland Assembly, established in 1998, has been suspended multiple times but was restored on 8 May, 2007. Northern Ireland's legal system descends from the pre-1920 Irish legal system (as does the legal system of the Republic of Ireland), and is therefore based on common law. It is separate from the jurisdictions of England and Wales or Scotland.

Northern Ireland has been for many years the site of a violent and bitter ethno-political conflict between those claiming to represent Nationalists, who are predominantly Catholic, and those claiming to represent Unionists, who are predominantly Protestant. In general, Nationalists want Northern Ireland to be unified with the Republic of Ireland, and Unionists want it to remain part of the United Kingdom. Unionists are in the majority in Northern Ireland, though Nationalists represent a significant minority. In general, Protestants consider themselves British and Catholics see themselves as Irish but there are some who see themselves as both British and Irish. People from Northern Ireland are entitled to both British and Irish citizenship (see Citizenship and Identity). The campaigns of violence have become known popularly as The Troubles. The majority of both sides of the community have had no direct involvement in the violent campaigns waged. Since the signing of the Belfast Agreement (also known as the Good Friday Agreement or the G.F.A.) in 1998, many of the major paramilitary campaigns have either been on ceasefire or have declared their war to be over.