The SDLP is the largest nationalist party in Northern Ireland.
The party is left of centre and has always espoused non-violence in the pursuit of its aims. It also has been a long-standing critic of all paramilitary groups and the British military presence in Northern Ireland.
The party has three MPs including party leader John Hume. At the 1997 General Election it won 24% of the vote in Northern Ireland.
Mr Hume was instrumental in getting the peace process under way by holding talks with Sinn Fein leader Gerry Adams and with the UK government.
His contribution was acknowledged in 1998 when he was jointly awarded the Nobel Peace Prize with Northern Ireland First Minister David Trimble.
The SDLP won 24 seats in the assembly, making it the second-largest party.
Mr Hume declined to become Deputy First Minister, allowing his deputy, Seamus Mallon, to take up that post.
Mr Mallon "resigned" from the post in a dramatic speech on 15 July, 1999, after the Ulster Unionists refused to join the powersharing executive. His resignation was overturned, however, in November that year when the executive was finally set up.