Sinn Fin ( shin FAYN, Irish: [n fen]; English: "[We] Ourselves") is an Irish republican and democratic socialist political party active throughout both the Republic of Ireland and Northern Ireland.

The original Sinn Fin organisation was founded in 1905 by Arthur Griffith. Its members founded the First Dil and the revolutionary Irish Republic during the Irish War of Independence. The party split in the aftermath of the Irish Civil War, giving rise to the two traditionally dominant parties of Irish politics: Fianna Fil, and Cumann na nGaedheal (which became Fine Gael). The current Sinn Fin party took shape in 1970 after another split, the other faction eventually becoming the Workers' Party. During the Troubles, Sinn Fin was associated with the Provisional Irish Republican Army (IRA). For most of the conflict, there were broadcasting bans on Sinn Fin in the Irish media and in the British media. Although the party sat on local councils, it had a policy of abstentionism for the British parliament and the Irish parliament Dil ireann, standing for election but vowing not to take their seats. When Gerry Adams became party leader in 1983, electoral politics became increasingly important. In 1986, it dropped its abstentionist policy for the Dil; some members formed Republican Sinn Fin in protest. In the 1990s, Sinn Finunder the leadership of Adams and Martin McGuinnesswas involved in the Northern Ireland peace process. This led to the Good Friday Agreement and created the Northern Ireland Assembly. In 2006, it co-signed the St Andrews Agreement and accepted the Police Service of Northern Ireland.

Sinn Fin is the largest party in the Northern Ireland Assembly, having won the largest share of first-preference votes and the most seats in the May 2022 election, the first time an Irish nationalist/republican party has done so. From 2007 to 2022 it was the second-largest party in the Assembly, after the Democratic Unionist Party (DUP), and its members served as deputy First Minister in the power-sharing Northern Ireland Executive. In the UK House of Commons, Sinn Fin holds seven of Northern Ireland's seats; there, it continues to abstain from parliament. In Dil ireann it is the joint-largest party and is the main opposition, having won the largest share of first-preference votes in the February 2020 election.

The current party president is Mary Lou McDonald, who succeeded Gerry Adams in 2018.

Derry, officially Londonderry (), is the second-largest city in Northern Ireland and the fifth-largest city on the island of Ireland. The name Derry is an anglicisation of the Old Irish name Daire (modern Irish: Doire [ˈd̪ˠɛɾʲə]) meaning 'oak grove'. The old walled city lies on the west bank of the River Foyle, which is spanned by two road bridges and one footbridge. The city now covers both banks (Cityside on the west and Waterside on the east).

The population of the city was 83,652 at the 2001 Census, while the Derry Urban Area had a population of 90,736. The district administered by Derry City and Strabane District Council contains both Londonderry Port and City of Derry Airport. Derry is close to the border with County Donegal, with which it has had a close link for many centuries. The person traditionally seen as the founder of the original Derry is Saint Colmcille, a holy man from Tír Chonaill, the old name for almost all of modern County Donegal, of which the west bank of the Foyle was a part before 1610.In 2013, Derry was the inaugural UK City of Culture, having been awarded the title in 2010.