Republican Sinn Féin (Irish: Sinn Féin Poblachtach), an unregistered Irish Republican political organisation, is founded at the West County Hotel in Dublin on November 2, 1986.

Republican Sinn Féin (RSF) claim to be heirs of the Sinn Féin party founded in 1905 and take its present form in 1986 following a split with Provisional Sinn Féin. RSF members take seats when elected in local Irish councils but do not recognise the partition of Ireland and subsequently the legitimacy of the Northern Ireland or Republic of Ireland governments, so does not register itself under them.

The decision to form, or to reorganise or reconstitute as its supporters see it, the organisation was taken in response to Gerry Adams-led Sinn Féin’s decision at its 1986 ardfheis to end its policy of abstentionism and to allow elected Sinn Féin Teachtaí Dála take their seats in Leinster House‘s Dáil Éireann. The supporters of Ruairí Ó Brádaigh and Dáithí Ó Conaill who go on to form RSF oppose this move as it signals a departure from the traditional republican analysis which views the parliament of the Republic of Ireland as an illegal assembly, set up by an act of the British parliament. They argue that republicans owe their allegiance to the All-Ireland (32 County) Irish Republic, maintaining that this state exists de jure and that its authority rests with the IRA Army Council. Hence, if elected, its members refuse to take their seats in the Oireachtas.

The organisation views itself as representing “true” or “traditional” Irish republicanism, while in the mainstream media the organisation is portrayed as a political expression of “dissident republicanism.” Republican Sinn Féin rejects the Good Friday Agreement and indeed the Anglo-Irish Treaty. As part of this they refuse to discount Irish republicans using militant means to “defend the Irish Republic” and considers the Continuity Irish Republican Army (IRA) to be the legitimate army of the Irish Republic. The CIRA is designated as a terrorist organisation by the governments of the United Kingdom and Republic of Ireland.