Claim: For most of the twentieth century, the Republic of Ireland and Northern Ireland had no formal relations.

Ireland -LRB- -LSB- ˈaɪərlənd -RSB- Éire -LSB- ˈeːɾʲə -RSB- -RRB- , also described as the Republic of Ireland -LRB- Poblacht na hÉireann -RRB- , is a sovereign state in north-western Europe occupying 26 of 32 counties of the island of Ireland . The capital and largest city is Dublin , which is located on the eastern part of the island , and whose metropolitan area is home to around a third of the country 's 4.75 million inhabitants . The state shares its only land border with Northern Ireland , a part of the United Kingdom . It is otherwise surrounded by the Atlantic Ocean , with the Celtic Sea to the south , Saint George 's Channel to the south-east , and the Irish Sea to the east . It is a unitary , parliamentary republic . The legislature , the Oireachtas , consists of a lower house , Dáil Éireann , an upper house , Seanad Éireann , and an elected President -LRB- Uachtarán -RRB- who serves as the largely ceremonial head of state , but with some important powers and duties . The head of government is the Taoiseach -LRB- Prime Minister , literally ` Chief ' , a title not used in English -RRB- , who is elected by the Dáil and appointed by the President ; the Taoiseach in turn appoints other government ministers .   The state was created as the Irish Free State in 1922 as a result of the Anglo-Irish Treaty . It had the status of dominion until 1937 when a new constitution was adopted , in which the state was named `` Ireland '' and effectively became a republic , with an elected non-executive president as head of state . It was officially declared a republic in 1949 , following the Republic of Ireland Act 1948 . Ireland became a member of the United Nations in December 1955 . It joined the European Economic Community -LRB- EEC -RRB- , the predecessor of the European Union , in 1973 . The state had no formal relations with Northern Ireland for most of the twentieth century , but during the 1980s and 1990s the British and Irish governments worked with the Northern Ireland parties towards a resolution to `` the Troubles '' . Since the signing of the Good Friday Agreement in 1998 , the Irish government and Northern Ireland Executive have co-operated on a number of policy areas under the North-South Ministerial Council created by the Agreement .   Ireland ranks among the top twenty-five wealthiest countries in the world in terms of GDP per capita , and as the tenth most prosperous country in the world according to The Legatum Prosperity Index 2015 . After joining the EEC , Ireland enacted a series of liberal economic policies that resulted in rapid economic growth . The country achieved considerable prosperity between the years of 1995 and 2007 , which became known as the Celtic Tiger period . This was halted by an unprecedented financial crisis that began in 2008 , in conjunction with the concurrent global economic crash . However , as the Irish economy was the fastest growing in the EU in 2015 , Ireland is again quickly ascending league tables comparing wealth and prosperity internationally . For example , in 2015 , Ireland was ranked as the joint sixth -LRB- with Germany -RRB- most developed country in the world by the United Nations Human Development Index . It also performs well in several national performance metrics , including freedom of the press , economic freedom and civil liberties . Ireland is a member of the European Union and is a founding member of the Council of Europe and the OECD . The Irish government has followed a policy of military neutrality through non-alignment since immediately prior to World War II and the country is consequently not a member of NATO , although it is a member in Partnership for Peace .