Ireland�s population descends from a variety of ethnic groups and reflects intermixing over millennia by successive waves of immigrants. Ireland�s population is predominantly of Celtic origin (Celts), but ancient tribes had inhabited Ireland for thousands of years when Celtic peoples settled the island in the 4th century bc. Over the centuries Ireland absorbed significant numbers of Vikings, Normans, and English. More recently, Ireland�s membership in the European Union (EU) has increased the number of citizens of other European countries living in Ireland, and small communities of ethnic Chinese and Indian people also have been established. Since 1996 Ireland has received small numbers of refugees and asylum seekers from eastern Europe, Africa, and Asia. Ireland also has a small indigenous minority known as Travellers. Numbering approximately 25,000, Travellers move and camp across the Irish countryside in small groups or cluster in enclaves within cities.

The population of the Irish Republic in 2005 was estimated at 4,015,676, giving the country an overall population density of 58 persons per sq km (151 per sq mi). Some 60 percent of the population lived in urban areas in 2003. The urban share of the population has increased with each successive census since 1926; the urban population exceeded the rural population for the first time in 1971.

Ireland�s economic growth in recent decades has reversed a long historical trend of emigration. For more than a century after the Great Potato Famine of the 1840s, Ireland�s population steadily declined, despite the nation�s relatively high birth rate. This continuous decline resulted from mass emigration, initially to escape the famine and later to seek employment and better lives, mainly in the United States and in the industrialized cities of the United Kingdom. In the 1960s and 1970s emigration fell sharply and no longer offset the natural increase. By the 1980s Ireland�s population was growing at an annual rate of about 0.5 percent, and in the 1990s immigration began to exceed emigration by a small margin. In 2002 Ireland�s population grew at an annual rate of 1.16 percent, one of the highest rates in western Europe.

Religious affiliation is remarkably uniform in Ireland: 85 percent of the population is Roman Catholic. However, this figure masks a steep and continuing decline in church attendance, particularly in urban areas and among young people. At the same time, the Roman Catholic Church in Ireland has experienced marked difficulties in recruiting clergy. Protestant groups include the Church of Ireland (Anglican) and the Presbyterian and Methodist denominations. Ireland�s constitution guarantees freedom of worship.

Almost all the people of Ireland speak English, and about one-fourth also claim to speak Irish, a Gaelic tongue that belongs to the family of Celtic languages. The Irish language, with its many regional variations, was once spoken by nearly all the Irish. Today, Irish is spoken on a daily basis by an estimated 30,000 people, most of whom live in the Gaeltacht (Gaelic-speaking) areas of the western seaboard. All government-subsidized schools in Ireland have taught Irish since 1922, but fewer than 10,000 pupils speak it as their first language. The constitution provides for both Irish and English as official languages, while Ulster-Scots (or Ullans), used by some members of Ireland�s Protestant community, is under consideration for special status.