Irish (Gaeilge), also known as Irish Gaelic, is a Goidelic language of the Indo-European language family, originating in Ireland and historically spoken by the Irish people. Irish is now spoken as a first language by a minority of Irish people, as well as being a second language of a larger proportion of the population. Irish enjoys constitutional status as the national and first official language of the Republic of Ireland. It is an official language of the European Union and an officially recognised minority language in Northern Ireland.

Irish was the predominant language of the Irish people for most of their recorded history, and they brought their Gaelic speech with them to other countries, notably Scotland and the Isle of Man, where it gave rise to Scottish Gaelic and Manx. It has the oldest vernacular literature in Western Europe. It began to decline under English and British rule after the seventeenth century. The nineteenth century saw a dramatic decrease in the number of speakers especially after the Great Famine of 1845–1852 (where Ireland lost 20–25% of its population either to emigration or death). Irish-speaking areas were especially hard hit. By the end of British rule, the language was spoken by less than 15% of the national population. Since then, Irish speakers have been in the minority except in areas collectively known as the Gaeltacht. Ongoing efforts have been made to preserve, promote and revive the language, particularly the Gaelic Revival.

The Irish people (Irish: Muintir na hÉireann or na hÉireannaigh; Ulster-Scots: Airisch or Airish fowk) are an ethnic group who originate in Ireland, an island in northwestern Europe. Ireland has been populated for around 9,000 years (according to archaeological studies, see Prehistoric Ireland). The Irish people's earliest ancestors are recorded in legends – they are claimed to be descended from groups such as the Nemedians, Fomorians, Fir Bolg, Tuatha Dé Danann and the Milesians.Lebor Gabála Érenn, a book of Irish mythology tells that Tuatha Dé Dananns were Scythian descendants.

The main groups that interacted with the Irish in the Middle Ages include the Picts, Scots, and the Vikings. Due to this contact, Icelanders are noted for having some Irish descent. The Anglo-Norman invasion of the High Middle Ages, the English plantations and the subsequent English rule of the country introduced the Normans and Flemish into Ireland. Welsh, Picts, Bretons, and small parties of Gauls and even Anglo-Saxons are known in Ireland from much earlier times.