There are a number of languages used in Ireland. Since the late 18th century, English has been the predominant first language, displacing Irish. A large minority claims some ability to use Irish, and it is the first language for a small percentage of the population.

In the Republic of Ireland, under the Constitution of Ireland, both languages have official status, with Irish being the national and first official language.

In Northern Ireland, English is the primary language for 95% of the population, and de facto official language, while Irish is recognised as an official language and Ulster Scots is recognised as a minority language under the Identity and Language (Northern Ireland) Act 2022.

The first linguistic records in Ireland are Primitive Irish inscriptions written in the Ogham alphabet. Scholars generally estimate that the earliest of these inscriptions were made in the fourth century CE. Languages spoken in Iron Age Ireland before then are now irretrievable, although there are some claims of traces in Irish toponymy.

Middle English was first introduced by the Cambro-Norman settlers in the 12th century. It did not initially take hold as a widely spoken language, as the Norman elite spoke Anglo-Norman. In time, many Norman settlers intermarried and assimilated to the Irish cultures and some even became "more Irish than the Irish themselves". Following the Tudor conquest of Ireland and the 1610–15 Ulster Plantation, particularly in the old Pale, Elizabethan English became the language of court, justice, administration, business, trade and of the landed gentry. Monolingual Irish speakers were generally of the poorer and less educated classes with no land. Irish was accepted as a vernacular language, but then as now, fluency in English was an essential element for those who wanted social mobility and personal advancement. After the legislative Union of Great Britain and Ireland's succession of Irish Education Acts that sponsored the Irish national schools and provided free public primary education, Hiberno-English replaced the Irish language. Since the 1850s, English medium education was promoted by both the UK administration and the Roman Catholic Church. This greatly assisted the waves of immigrants forced to seek new lives in the US and throughout the Empire after the Famine. Since then the various local Hiberno-English dialects comprise the vernacular language throughout the island.

The 2002 census found that 103,000 British citizens were living in the Republic of Ireland, along with 11,300 from the US and 8,900 from Nigeria, all of whom would speak other dialects of English. The 2006 census listed 165,000 people from the UK, and 22,000 from the US. The 2016 census reported a decline in UK nationals to the 2002 level: 103,113.

The original Primitive Irish was introduced by Celtic speakers. Primitive Irish gradually evolved into Old Irish, spoken between the 5th and the 10th centuries, and then into Middle Irish. Middle Irish was spoken in Ireland, Scotland, and the Isle of Man through the 12th century, when it began to evolve into modern Irish in Ireland, Scottish Gaelic in Scotland, and the Manx language in the Isle of Man. Today, Irish is recognized as the first official language of the Republic of Ireland and is officially recognized in the European Union. Communities that speak Irish as their first language, generally in sporadic regions on the island's west coast, are collectively called the Gaeltacht.

In the 2016 Irish census, 8,068 census forms were completed in Irish, and just under 74,000 of the total (1.7%) said they spoke it daily. The total number of people who answered 'yes' to being able to speak Irish to some extent in April 2016 was 1,761,420, 39.8 percent of respondents.