Ireland has a longstanding policy of military neutrality, which has meant not joining military alliances or defence pacts, or taking part in international conflicts. Irish neutrality is in general a matter of government policy rather than a requirement of statute law, with the 1937 constitution not defining neutrality as an aim of the state, and its nature has varied over time.
The Irish Free State declared itself a neutral country in 1922, and Ireland remained neutral during the Second World War; although it allowed Allied military aircraft to fly through part of its airspace, and shared intelligence with the Allies (see Irish neutrality during World War II). During the Cold War, it did not join NATO nor the Non-Aligned Movement.Tonra et al. 2012, Preface: The Study of Irish Foreign Policy p.xix Since the 1970s, some have defined Irish neutrality more broadly to include a commitment to "United Nations peacekeeping, human rights and disarmament". Recent Irish governments have defined it narrowly as non-membership of military alliances.
Ireland is one of four European Union countries that are not members of NATO; the others are Austria, Cyprus and Malta. The compatibility of neutrality with Ireland's EU membership has been a point of debate in EU treaty referendum campaigns since the 1990s. The Seville Declarations on the Treaty of Nice acknowledge Ireland's "traditional policy of military neutrality".Seville Declarations on the Nice Treaty The Irish Defence Forces have been involved in many UN peacekeeping missions.
Concept There are notable differences between Irish neutrality and “traditional” types of neutral states: Traditionally, neutral states maintain strong defence forces; Ireland has a relatively small defence force of approximately 10,500 personnel. Traditionally, neutral states do not allow any foreign military within their territory; Ireland has a long history of allowing military aircraft of various nations to refuel at Shannon Airport. Under the Air Navigation (Foreign Military Aircraft) Order, 1952, the Minister for Foreign Affairs, exceptionally, could grant permission to foreign military aircraft to overfly or land in the state. Confirmation was required that the aircraft in question be unarmed, carry no arms, ammunition or explosives and that the flights in question would not form part of military exercises or operations.
After the September 11 attacks, these conditions were "waived in respect of aircraft operating in pursuit of the implementation of the United Nations Security Council Resolution 1368". Irish governments have always said that allowing aircraft to use Irish soil does not constitute participation in any particular conflict and is compatible with a neutral stance, adducing the transit of German troops between Finland and Norway through neutral Swedish territory during World War II.
A neutral state may also allow its citizens to serve in the armed forces of other, possibly belligerent, nations. Ireland does not restrict its citizens from serving in foreign armies, and significant numbers of Irish citizens serve or have served in the British, and to a lesser extent United States armies and the French Foreign Legion.
Legal status
Ireland's neutrality is in general a matter of government policy rather than a requirement of statute law. One exception is Article 29.4.9° of the Irish constitution:
This was originally inserted by the 2002 amendment ratifying the Treaty of Nice, and updated by the 2009 amendment ratifying the Treaty of Lisbon. An earlier bill intended to ratify the Treaty of Nice did not include a common defence opt-out, and was rejected in the first Nice referendum, in 2001.
Other European Union member states have also maintained neutrality or military non-alignment alongside EU membership. Malta's constitution provides that "Malta is a neutral state" pursuing a policy of non-alignment and "refusing to participate in any military alliance", while Austria declared permanent neutrality in 1955. The Treaty on European Union provides that a common Union defence would require a unanimous decision of the European Council and adoption by member states "in accordance with their respective constitutional requirements", and states that EU security and defence policy "shall not prejudice the specific character of the security and defence policy of certain Member States".
The Defence Act 1954, the principal statute governing the Irish Defence Forces, did not oblige members of the Irish Army to serve outside the state (members of the Air Corps and Naval Service were not so limited). A 1960 amendment replacing the temporary was intended to allow deployment in United Nations peacekeeping missions, and requires three forms of authorisation, which since the 1990s have come to be called the "triple lock": A UN Security Council resolution or UN General Assembly resolution; A formal decision by the Irish government; Approval by a resolution of Dáil Éireann (the lower house of the Oireachtas or parliament, to which the government is responsible).
These provisions were modified in 1993 to allow for Chapter VII missions and again in 2006, when an "International United Nations Force" was defined to include an international force or body "established, mandated, authorised, endorsed, supported, approved or otherwise sanctioned" by a resolution of either the Security Council or the General Assembly. The General Assembly has authorised or mandated peace operations in the past, including the United Nations Emergency Force in 1956, the United Nations Temporary Executive Authority in West New Guinea in 1962, a joint United Nations/regional peace operation in Haiti in 1993, and a peace operation in Guatemala in the 1990s.
In 2025, the government proposed to eliminate the requirement of a UN mandate. Government arguments for reform have centred on the veto power of the permanent members of the Security Council. In March 2025, the Department of Defence said proposed amendments would remove "the power of UN Security Council permanent members to veto our national sovereign decisions", while also increasing the number of Defence Forces personnel that could be deployed without a Dáil resolution from twelve to fifty. In a Dáil debate in May 2026, a Government speaker said that the existing system "effectively allows permanent members of the Security Council to bind Ireland's hands in its international engagement". The statutory definition introduced in 2006, however, refers to a force or body sanctioned by a resolution of either the Security Council or the General Assembly.
A cited example was the 1999 Chinese veto of the renewal of the United Nations Preventive Deployment Force in Macedonia; the Security Council draft resolution had received thirteen votes in favour, with China voting against and Russia abstaining. In 2023, the Irish government stated that because the subsequent European Union peace operation in the former Yugoslav Republic of Macedonia, fYROM/CONCORDIA, did not have a Security Council mandate, Ireland was unable to participate in that mission.
History
Before independence
Irish leaders in the Nine Years' War (1594–1603) allied with Habsburg Spain, who sent military aid to the Irish. Following their defeat, all of Ireland was a dependency of England and then of Great Britain. During this period, Catholic soldiers from Ireland fought in the armies of several European Catholic countries, in what is known as the Flight of the Wild Geese. In 1644–1645, during the Wars of the Three Kingdoms, the Irish Confederacy sent a military expedition to Scotland to help the Scottish Royalists. During the Irish Rebellion of 1798, the United Irishmen sought and received military assistance from the French First Republic.
Ireland was part of the United Kingdom of Great Britain and Ireland from 1801 to 1922. While Irish unionists supported political integration with Britain, Irish nationalists were divided between those who envisaged some continuing link with Britain and the "advanced nationalists", mainly republicans, who wanted full independence. Separatists generally envisaged an independent Ireland being neutral, but were prepared to ally with Britain's enemies in order to secure that independence, reflected in the maxim "England's difficulty is Ireland's opportunity".Fanning 1982, p.27 At the outbreak of the First World War, James Connolly was president of the Irish Neutrality LeagueFanning 1982, p.28 and was prosecuted for a banner reading "We serve neither King nor Kaiser but Ireland". During the 1916 Easter Rising, Connolly and the other leaders of the uprising sought military aid from Germany.
In the 1921 negotiations leading to the Anglo-Irish Treaty, Erskine Childers envisaged the Irish Republic having a neutral status guaranteed in international law on the model of Belgium and Switzerland.
Irish Free State The Irish Free State established in 1922 by the Anglo-Irish Treaty was a Dominion of the British Commonwealth, with the UK retaining responsibility for Ireland's marine defence as well as three naval bases, the "Treaty Ports". Article 49 of the 1922 Constitution of the Irish Free State stated, "Save in the case of actual invasion, the Irish Free State ... shall not be committed to active participation in any war without the assent of the Oireachtas [parliament]". In the 3rd Dáil debate on the draft constitution, the Provisional Government rejected a Labour Party amendment requiring assent of the electorate via referendum. Thomas Johnson argued "The war that is to be guarded against is a war overseas, is a war that this country may be drawn into by Parliament, by the will of Parliament perhaps, at the instigation of perhaps Canada, or perhaps Australia, or perhaps South Africa, or perhaps Great Britain, and the last is very much the more likely".
In the Statute of Westminster 1931, the UK renounced the right to legislate for the Free State. The 1938 Anglo-Irish Trade Agreement saw the Treaty Ports handed over to the Free State.
The Free State joined the International Committee for Non-Intervention in the Spanish Civil War. The Spanish Civil War (Non-Intervention) Act, 1937 made it an offence to travel from Ireland to Spain to fight for either side. This applied both to Irish citizens and nationals of other countries on the committee. Nevertheless, there was Irish involvement in the Spanish Civil War on both sides by private individuals and groups. Another statute related to the committee was the Merchant Shipping (Spanish Civil War) Act 1937, which restricted Irish shipping's access to Spain until 27 April 1939.
World War II
Ireland remained neutral during World War II. The Fianna Fáil government's position was flagged years in advance by Taoiseach Éamon de Valera and had broad support. James Dillon was the only member of Dáil Éireann to oppose it during the war, resigning from Fine Gael in 1942 and demanding that Ireland assist the Allies (while not necessarily declaring war on the Axis). However, tens of thousands of Irish citizens, who were by law British subjects, fought in the Allied armies against the Nazis, mostly in the British army. Senators John Keane and Frank MacDermot also favoured Allied support.