Ireland (// ( listen); Irish: Éire ( listen); Ulster-Scots: Airlann ) is an island in the North Atlantic. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the third-largest island in Europe. It is the second largest island in the British Isles, after Great Britain.
Politically, Ireland is divided between the Republic of Ireland (officially named Ireland), which covers five-sixths of the island, and Northern Ireland, which is part of the United Kingdom, in the northeast of the island. In 2011, the population of Ireland was about 6.6 million, ranking it the second-most populous island in Europe after Great Britain. Just under 4.8 million live in the Republic of Ireland and just over 1.8 million live in Northern Ireland.
The island's geography comprises relatively low-lying mountains surrounding a central plain, with several navigable rivers extending inland. The island has lush vegetation, a product of its mild but changeable climate which is free of extremes in temperature. Thick woodlands covered the island until the Middle Ages. As of 2013, the amount of land that is wooded in Ireland is about 11% of the total, compared with a European average of 35%. There are twenty-six extant mammal species native to Ireland. The Irish climate is very moderate and classified as oceanic. As a result, winters are milder than expected for such a northerly area. However, summers are cooler than those in Continental Europe. Rainfall and cloud cover are abundant.
The earliest evidence of human presence in Ireland is dated at 10,500 BC. Gaelic Ireland had emerged by the 1st century CE. The island was Christianised from the 5th century onward. Following the Norman invasion in the 12th century, England claimed sovereignty over Ireland. However, English rule did not extend over the whole island until the 16th–17th century Tudor conquest, which led to colonisation by settlers from Britain. In the 1690s, a system of Protestant English rule was designed to materially disadvantage the Catholic majority and Protestant dissenters, and was extended during the 18th century. With the Acts of Union in 1801, Ireland became a part of the United Kingdom. A war of independence in the early 20th century was followed by the partition of the island, creating the Irish Free State, which became increasingly sovereign over the following decades, and Northern Ireland, which remained a part of the United Kingdom. Northern Ireland saw much civil unrest from the late 1960s until the 1990s. This subsided following a political agreement in 1998. In 1973 the Republic of Ireland joined the European Economic Community while the United Kingdom, and Northern Ireland, as part of it, did the same.
Irish culture has had a significant influence on other cultures, especially in the fields of literature. Alongside mainstream Western culture, a strong indigenous culture exists, as expressed through Gaelic games, Irish music, and the Irish language. The culture of the island also shares many features with that of Great Britain, including the English language, and sports such as association football, rugby, horse racing, and golf.
The name Ireland derives from Old Irish Eriu. This in turn comes from the Proto-Celtic *Iveriu (compare Welsh Iwerddon), which is also the source of Latin Hibernia. Iveriu derives from a root meaning 'fat, prosperous'.
During the last glacial period, and up until about 10,000 BC, most of Ireland was periodically covered in ice. Sea levels were lower and Ireland, like Great Britain, formed part of continental Europe. By 16,000 BC, rising sea levels due to ice melting caused Ireland to become separated from Great Britain. Later, around 6000 BC, Great Britain itself became separated from continental Europe. The earliest evidence of human presence in Ireland is dated at 10,500 BC, demonstrated by a butchered bear bone found in a cave in County Clare. It is not until about 8000 BC, however, that more sustained occupation of the island has been shown, with evidence for Mesolithic communities around the island. These Mesolithic communities lived as hunter-gatherers across the island until about 4000 BC.