Founded in the early 1970s, the SDLP was the largest nationalist party in Northern Ireland during the Troubles.
It has since been overtaken by Sinn Fein in the polls, but remains second largest Northern Ireland party at Westminster by virtue of Sinn Fein's continued abstention.
The party is left of centre and in contrast to Sinn Fein has always espoused non-violence in the pursuit of its aims. It has been a long-standing critic of all paramilitary groups and the British military presence in Northern Ireland.
Party leader John 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 then Northern Ireland First Minister David Trimble.