Ireland is an island in the North Atlantic Ocean, west of the European mainland, divided into two countries: Ireland, occupying five-sixths of the island of Ireland, west of Great Britain, and Northern Ireland, part of the United Kingdom. This island has a strategic location on major air and sea routes between North America and northern Europe. Over 40% of the population resides within 100 km of Dublin. The coastline is about 1450 km.

The four provinces probably in ancient times have been five, as indicated by the Irish word for the provinces, cóiceda (which means fifths). These are Ulster (Ulaid), Connacht, Munster (Mumu), Leinster (Lagin) and Meath (Mide).