Ireland 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 second-largest island of the British Isles, the third-largest in Europe, and the twentieth-largest on Earth.
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 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. Its lush vegetation is a product of its mild but changeable climate which is free of extremes in temperature. It was covered by thick woodlands 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 influenced by the Atlantic Ocean and thus very moderate, and winters are milder than expected for such a northerly area, although 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 (12,500 years ago). Gaelic Ireland had emerged by the 1st century AD. The island was Christianised from the 5th century onward. Following the 12th century Norman invasion, England claimed sovereignty. 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 island's culture shares many features with that of Great Britain, including the English language, and sports such as association football, rugby, horse racing, and golf.
Ireland is located in the north-west of Europe, between latitudes 51° and 56° N, and longitudes 11° and 5° W. It is separated from Great Britain by the Irish Sea and the North Channel, which has a width of 23 kilometers (14 mi) at its narrowest point. To the west is the northern Atlantic Ocean and to the south is the Celtic Sea, which lies between Ireland and Brittany, in France. Ireland has a total area of 84,421 km2 (32,595 sq mi), of which the Republic of Ireland occupies 83 percent. Ireland and Great Britain, together with many nearby smaller islands, are known collectively as the British Isles. As the term British Isles is controversial in relation to Ireland, the alternate term Britain and Ireland is often used as a neutral term for the islands.
A ring of coastal mountains surround low plains at the centre of the island. The highest of these is Carrauntoohil (Irish: Corrán Tuathail) in County Kerry, which rises to 1,038 m (3,406 ft) above sea level. The most arable land lies in the province of Leinster. Western areas can be mountainous and rocky with green panoramic vistas. The River Shannon, the island's longest river at 386 km (240 mi) long, rises in County Cavan in the north west and flows 113 kilometres (70 mi) to Limerick city in the mid west.