Northern Ireland ( ; Ulster Scots: ) is a constituent unit of the United Kingdom of Great Britain and Northern Ireland in the northeast of the island of Ireland. It is variously described as a country, province, region, or "part" of the United Kingdom, amongst other terms. Northern Ireland shares a border to the south and west with the Republic of Ireland. In 2011, its population was 1,810,863, constituting about 30% of the island's total population and about 3% of the UK's population. Established by the Northern Ireland Act 1998 as part of the Good Friday Agreement, the Northern Ireland Assembly holds responsibility for a range of devolved policy matters, while other areas are reserved for the British government. Northern Ireland co-operates with the Republic of Ireland in some areas, and the Agreement granted the Republic the ability to "put forward views and proposals" with "determined efforts to resolve disagreements between the two governments".

The people of Northern Ireland are "all persons born in Northern Ireland and having, at the time of their birth, at least one parent who is a British citizen, an Irish citizen or is otherwise entitled to reside in Northern Ireland without any restriction on their period of residence," under the Belfast Agreement.