Republican Sinn Féin or RSF (Irish: Sinn Féin Poblachtach) is an Irish republican political party in Ireland. RSF claims to be heirs of the Sinn Féin party founded in 1905 and took its present form in 1986 following a split in Sinn Féin. RSF members take seats when elected to local government in the Republic of Ireland, but do not recognise the validity of the Partition of Ireland. It subsequently does not recognise the legitimacy of the parliaments of Northern Ireland (Stormont) or the Republic of Ireland (Leinster House), so the party does not register itself with them.

The party emerged around the supporters of Ruairí Ó Brádaigh and Dáithí Ó Conaill. As Irish republican legitimists, they rejected the reformism of Gerry Adams and other members of Sinn Féin who supported abandoning the policy of abstentionism from the Oireachtas and accepting the legality of the Republic of Ireland. They support the Éire Nua policy which allows for devolution of power to provincial governments. RSF holds that the Irish Republic proclaimed in 1916 legally continues to exist, and that the Continuity Irish Republican Army Council is its de jure government.

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 the Anglo-Irish Treaty; as part of this they assert that Irish republicans have the right to use militant means to "defend the Irish Republic" and considers the Continuity Irish Republican Army (IRA) to be the legitimate army of the Irish Republic, and the Continuity IRA Army Council its legal government.