Margaret Ritchie is the fourth leader of the SDLP
The SDLP - Social Democratic and Labour Party - was born in 1970 out of the civil rights movement which came before the Troubles.
It draws its support mainly from Catholics and nationalists.
Many of its founding members, drawn mainly from the Nationalist Party, the National Democratic Party and Republican Labour, were key figures in the civil rights campaigns.
The campaigns grew around Northern Ireland as Catholics demanded an end to what they saw as sectarian government.
The SDLP made history in 1997 when one of its councillors, Alban Maginness, became the first nationalist to be appointed Lord Mayor of Belfast.
Former leaders John Hume and Mark Durkan are seen as two of the main architects of the Good Friday Agreement.
The SDLP was the dominant political force among Northern Ireland nationalists until 2003 when it was overtaken by Sinn Fein at the Northern Ireland Assembly election.
The party has historically had close links with Britain's Labour Party.
It takes a strong pro-Europe line and favours entry to the single currency.
In 2010, the party elected Margaret Ritchie, Assembly Member for South Down, as its new leader.
She was appointed Minister for Social Development in May 2007 and is the sole SDLP member of the Northern Ireland Executive.
In the 40-year history of the SDLP, Ms Ritchie has served in a ministerial role longer than any other member.
The SDLP leader has plans to take over from Eddie McGrady as South Down MP.
Mr McGrady has said he will not be standing in the upcoming General Election.
The SDLP representative is stepping down from the seat he has represented at Westminster since 1987.
The 74-year-old said that after 50 years as a councillor, assembly member and MP he had "recently" decided it was time to step down.
In the recent MPs expenses scandal, Mr McGrady was asked by the independent auditor Sir Thomas Legg to pay back £3,854 for hotel bills.
The SDLP's Alasdair McDonnell was elected the MP for South Belfast in 2005.
The party's former leader, Mark Durkan, will contest Foyle. He has been the MP for Foyle since 2005. Mr Durkan, 49, replaced John Hume as leader of the party in 2001.
In the 2007 assembly election, the SDLP lost more ground winning 16 seats, leaving Sinn Fein on 28 seats.
While it supports the principle of a united Ireland, the party stresses that this cannot come about without the consent of the people.
Since an internal review suggested it was losing voters to Sinn Fein because of its "tired and middle class image", it has tried to modernise itself to attract more young and non-Catholic voters.
A new face for the SDLP is the former UTV reporter Fearghal McKinney who has said he intends to stand for the SDLP in Fermanagh and South Tyrone.
Ms Ritchie said of the move that she was fulfilling her promise to bring through "a new generation of SDLP representatives".