Goidelic is one of two major divisions of modern-day Celtic languages (the other being Brythonic). Also known as Gaelic, or Q-Celtic for the way it uses a "C" or "K" to begin words that, in the hypothetical base Indo-european language, began with "Qu" (in contrast with Brythonic, which changed the sound much more severely to a "P").

The three Goidelic languages to survive into modern times are Irish Gaelic, Scots Gaelic, and Manx. Goidelic languages were once restricted to Ireland, but in the 6th century Irish colonists and invaders began migrating to Scotland and slowly pushed out the Brythonic language found there. Manx is in turn an offshoot of Scottish Gaelic, with heavy influence from Norse from the time the Isle of Man was controlled by Viking Scandinavians. Goidelic languages were once common on the western edge of Celtic Europe; there is also evidence that they were spoken in the region of Galicia in Spain.

Irish Gaelic, (known as 'Irish', formerly 'Erse'), is one of Ireland's two official languages and is still fairly widely spoken in the west of Ireland. An Irish speaking area is called a Gaeltacht and they are to be found in Counties Donegal, Mayo, Galway, Kerry and, to a lesser extent, in Waterford and Meath. Scots Gaelic is still spoken to some extent in the north and west of Scotland and the Hebrides but partly because of its lack of official recognition and partly because of large-scale emigration from this part of Scotland, there are not as many native speakers as there used to be. There are now believed to be 1000 native speakers of Scots Gaelic in Nova Scotia and 60000 in Scotland. Manx is the almost extinct language of the Isle of Man. However, attempts to revive it continue.

The other commonly used Celtic languages belong to the Brythonic branch of Celtic and include Welsh and Breton, as well as the nearly-extinct Cornish language.