The Republic of Ireland
Bunreacht na hÉireann, the constitution of Ireland, provides that "the name of the state is Éire, or, in the English language, "Ireland." The state is also described as the "Republic of Ireland," in order to distinguish it from the island of Ireland and from Northern Ireland. The Republic of Ireland Act defined Republic of Ireland as the description of the state in 1949 (the purpose of the act being to declare that the state was a republic rather than a form of constitutional monarchy). However, because this was a statutory provision, the constitutional name of "Ireland" remains the official name of the state, whilst "Republic of Ireland" is a description of the state. "Republic of Ireland" is also the accepted legal name of the state in the United Kingdom as per the Ireland Act 1949. Therefore it is the name Ireland that is used for official purposes such as treaties, government and legal documents, and membership of international organisations. However, with Irish being named the European Union's twenty-first official language in 2007; the state will be referred to in both constitutional official languages, the Irish and English languages, similarly to other countries such as Finland and Belgium using more than one language at EU level. This means the label 'Éire Ireland' will be used on various signage and nameplates referring to the state.

The state is also known by other names in English, such as Éire, The Free State, and the Twenty-six Counties. The use of Éire when speaking English in Ireland has become increasingly rare. Often in the United Kingdom, the state is referred to as Southern Ireland, though this term is used informally and was only used officially for a brief period in Irish history. Irish people sometimes refer to the state as "The South" - it is not uncommon to hear Northern Irish people talking about going "down south."

The state has had more than one official title. The revolutionary state, declared in 1919 by the large majority of Irish Members of (the United Kingdom) Parliament elected in 1918, was known as the "Irish Republic;" when the state achieved de jure independence in 1922, it became known as the "Irish Free State" (in the Irish language Saorstát Éireann), a name that was retained until 1937.

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 is, however, currently suspended. 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. 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 in 1998, many of the major paramilitary campaigns have either been on ceasefire or have declared their war to be over.