Devolution is the transfer of powers from central government to regional government.
Under the 1998 Belfast Agreement or Good Friday Agreement, the UK Parliament transferred legislative and executive powers to the Northern Ireland Assembly and Executive Committee. This is known as 'devolution' and it means that the Assembly and Executive Committee (also known as the Northern Ireland Executive) make laws and decisions on most of the issues affecting everyday life in Northern Ireland. These are called 'transferred matters' and they include health, education, roads and housing.
The Assembly is the legislature for Northern Ireland and it appoints the Executive Committee of Ministers to exercise excecutive authority or 'govern' Northern Ireland. Ministers head up Northern Ireland's 9 Government Departments.
Scotland and Wales also have devolved systems of government.
Westminster stills retains powers over issues affecting the whole of the UK, such as foreign affairs, income tax and immigration policy. These are known as 'reserved matters' or 'excepted matters'.