Republic of Ireland (Irish: Poblacht na hÉireann), is a sovereign state in Europe occupying about five-sixths of the island of Ireland. It is a unitary parliamentary republic with an elected president serving as head of state. The head of government—called the Taoiseach—is nominated by the lower house of parliament (Dáil Éireann). The capital is Dublin in the east of the island. The state shares its only land border with Northern Ireland, one of the constituent countries 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.