All-Ireland (sometimes All-Island) is a term used to describe organisations and events whose interests extend over the entire island of Ireland, as opposed to the separate jurisdictions of the Republic of Ireland and Northern Ireland. "All-Ireland" is most frequently used to refer to sporting teams or events for the entire island, but also has related meanings in politics and religion.

Many high profile modern sports were codified within the United Kingdom at the end of the nineteenth century, during a period of British imperial dominance, and while the whole of Ireland was a constituent country of the United Kingdom. As such, early international competition first featured the four constituent countries of the UK; England, Scotland, Wales and Ireland, before spreading to other parts of the Empire. For this reason, in many sporting contexts outside Olympic sport (which was first reorganised by the French and Greeks, and in which the UK competed as Great Britain), the UK does not compete as one national team, and almost never under the name 'United Kingdom'. When the Irish Free State left the United Kingdom in 1923, many of the existing 'Ireland' teams remained united, covering both jurisdictions, although association football, notably, did not. These sports are described as being organised on an All-Ireland or all-island basis.^{[failed verification]}

"The All-Ireland", with the definite article, is often used as an abbreviation of All-Ireland Championship, within Gaelic Games, most specifically

Many other sports are organised on an all-Ireland basis, most notably rugby union. Other such sports include American football, basketball, boxing, cricket, curling, Gaelic games, golf, hockey, lawn bowls, korfball, Quidditch and rugby league. The international team is usually referred to simply as "Ireland". Others are organised primarily on an all-Ireland basis, but with both "Ireland" and "Great Britain" international teams, in which case participants from Northern Ireland may opt for either — these include tennis, swimming, athletics, rowing and any events at the Olympics.

A small number of sports have separate Northern Ireland and (Republic of) Ireland organisations and teams, including notably football when for several years separate organisations — the Irish Football Association in Belfast, Northern Ireland (which undisputedly represented the island before the partition) and the Football Association of Ireland in Dublin, Ireland — named their teams 'Ireland' until FIFA were forced to settle the dispute and made each side go by distinguishable names. Until FIFA's intervention, many footballers played for both Irish representative teams.

Other sports with separate Northern Ireland administration and international recognition include netball and snooker.

Similarly to the example of Gaelic games, the term may be used in reference to annual competitions in certain Irish traditional music and art forms:

It is also used in the title Primate of All Ireland, the senior clergyman in each of the Roman Catholic Church and the Church of Ireland: