The Anglo-Irish War (also known as the Irish War of Independence) was a guerilla campaign mounted against the British government in Ireland by the Irish Republican Army. It lasted from about January 1919 until the truce in July 1921.

It had its origins in the formation of unilaterally created independent Irish parliament, called Dáil Éireann, formed by the majority of MPs elected in Irish constituencies in the Irish (UK) general election, 1918. This parliament, known as the First Dáil, and its ministry, called the Aireacht declared Irish independence. The IRA, as the 'army of the Irish Republic', was perceived by members of Dáil Éireann to have a mandate to wage war on the Dublin Castle British administration running Ireland.

Several different military and paramilitary forces fought on the British government side, including the Royal Irish Constabulary, the British Army, the Black and Tans and the Auxiliaries.

The Irish Republican Army which fought in this conflict is often referred to as the Old IRA to distinguish it from later, different, organisations that used the same name.

The war ended in a Truce in 1921, which led to the negotiation of the Anglo-Irish Treaty (1921) and the creation of the Irish Free State in 1922. A minority of those involved in the War of Independence refused to accept the Treaty and started the Irish Civil War which lasted until mid 1923 and which cost of the lives of some of the leaders of the independence movement, notably Michael Collins and Rory O'Connor.

A memorial called the Garden of Remembrance was erected in Dublin in 1966, the fiftieth anniversary of the Easter Rising. The date of signing of the truce is commemorated by the National Day of Commemoration