Sinn Fein used to be widely regarded as the political wing of the IRA, but today the party insists that the two organisations are completely separate.
A republican party devoted to establishing a united Ireland, Sinn Fein advocates strong cross-border bodies as a step towards achieving that goal and the maintenance of the Irish Republic's territorial claim to Northern Ireland.
It is a strong supporter of the Good Friday Agreement, but accuses unionists of undermining the deal in the months since it was signed.
The original Sinn Fein campaigned for an independent, united Ireland before and after the First World War. The current form of the party dates back to 1970 when Provisional Sinn Fein split away from Official Sinn Fein, which became the Workers' Party. This split mirrored the split in the IRA into Official and Provisional wings.
Since the early 1980s, Sinn Fein has slowly gained strength and political power. At the 1997 general election, it won 16% of the vote. Its two MPs, party president Gerry Adams and Martin McGuinness, have never sat at Westminster as they refuse to take the oath of allegiance to the Queen.
Sinn Fein has 18 seats in the Northern Ireland Assembly and two seats on the executive.
Sinn Fein was angered by the refusal of First Minister David Trimble to allow it to take up its executive seats until the IRA began to disarm, arguing that the Agreement gave it an automatic right to attend regardless of the IRA's actions.
In November 1999, however, Sinn Fein made a statement reaffirming its beliefs in decommissioning as an essential part of the peace process and in the IRA's commitment to a permanent peace. That statement - and similar declarations from the Ulster Unionists and the IRA - were seen as a breakthrough in the decommissioning deadlock.
Three months later, however, it became apparent that no decommissioning had taken place. Sinn Fein was angered by unionist pressure on the government and the suspension of the executive, arguing that this amounted to a unionist veto.
Sinn Fein welcomed the IRA's announcement in May 2000 that it was ready to put its weapons beyond use.