Céilí (pronounced Kay-Lee) is the traditional social Irish dance. In the old days, before discos and nightclubs, there were céilís in most town and village halls on Friday or Saturday nights. Céilís facilitated courting and prospects of marriage for young people. Although discos and nightclubs have displaced céilís to a considerable extent, they are still an important and popular social outlet in rural parts of Ireland, especially in the Gaelic-speaking westcoast regions. Céilís are sometimes held on a smaller scale in Public houses, for example in remote rural hinterlands and during busy festivals.

Céilí music is provided by any assortment of fiddle, flute, tin whistle, accordion, bodhrán (pronounced Bough-Rawn) which is a wooden frame covered with the stretched goat hide, and in more recent times also drums and electric bass guitar. The music is cheerful and lively and requires knowledge of basic "123 123" dance steps.

The general format of céilí dancing is the "Set". A Set consists of four couples, with each pair facing another in a square formation. Each couple exchanges position with the facing couple, and also facing couples exchange partners, while all the time keeping in step with the beat of the music.

There is also a form of line dancing, the "Siege of Ennis" being the most popular; some of the céilí dance formations are named after famous battles and events in Irish history.

"Step dancing" is another form of céilí dancing, the form that has been popularised in recent years by the world famous Riverdance emsemble. Whereas Set dancing involves all present, whatever their skill, Step dancing is usually reserved for show, being performed only by the most talented of dancers.

The céilí has been internationalised by the Irish diaspora in the United States and Australia, where local céilís and traditional music competitions are held. In recent years, Irish céilí and traditional music competitions have been frequently won by American or Australian descendants of Irish emigrants.

In Scotland, with its close cultural, linguistic and racial connections with Ireland, there are ceilidh (also pronounced Kay-Lee), which are very similar to the Irish céilís in terms of the music, the traditional facilitation of courting, and lots of lively fun.