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. 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. Although the Republic is not in any military alliance, it relies on a NATO member, the United Kingdom, to protect Irish airspace. In recent years, the UK has intercepted armed Russian bombers flying into Irish airspace. The Republic also allows stopovers by some foreign military aircraft, provided they are not armed.

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". The Irish Defence Forces have been involved in many UN peacekeeping missions.

There are notable differences between Irish neutrality and “traditional” types of neutral states:

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.

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:

The State shall not adopt a decision taken by the European Council to establish a common defence pursuant to Article 42 of the Treaty on European Union where that common defence would include the State.