The island of Ireland, comprising Northern Ireland and the Republic of Ireland, has an extensive network of tens of thousands of kilometres of public roads, usually surfaced. These roads have been developed and modernised over centuries, from trackways suitable only for walkers and horses, to surfaced roads including modern motorways. Driving is on the left-hand side of the road. The major routes were established before Irish independence and consequently take little cognisance of the border other than a change of identification number and street furniture. Northern Ireland has had motorways since 1962, and has a well-developed network of primary, secondary and local routes. The Republic started work on its motorway network in the early 1980s; and historically, the road network there was once somewhat less well developed. However, the Celtic Tiger economic boom and an influx of European Union structural funding, saw national roads and regional roads in the Republic come up to international standard quite quickly. In the mid-1990s, for example, the Republic went from having only a few short sections of motorway to a network of motorways, dual carriageways and other improvements on most major routes as part of a National Development Plan. Road construction in Northern Ireland now tends to proceed at a slower pace than in the Republic, although a number of important bypasses and upgrades to dual carriageway have recently been completed or are about to begin.

A regional road in the Republic of Ireland is a class of road not forming a major route, but nevertheless forming a link in the national route network. There are over 11,600 kilometres of regional roads. Regional roads are numbered with three-digit route numbers, prefixed by "R". The equivalent road category in Northern Ireland are B roads.