The phrase "Sinn Féin" is Irish for "Ourselves" or "We Ourselves", although it is frequently mistranslated as "ourselves alone" (from "Sinn Féin Amháin", an early-20th-century slogan). The name is an assertion of Irish national sovereignty and self-determination, i.e., the Irish people governing themselves, rather than being part of a political union with Great Britain under the Westminster Parliament.

A split in January 1970, mirroring a split in the IRA, led to the emergence of two groups calling themselves Sinn Féin. One, under the continued leadership of Tomás Mac Giolla, became known as "Sinn Féin (Gardiner Place)", or "Official Sinn Féin"; the other, led by Ruairí Ó Brádaigh, became known as "Sinn Féin (Kevin Street)", or "Provisional Sinn Féin". As the "Officials" dropped all mention of Sinn Féin from their name in 1982—instead calling themselves the Workers' Party—the term "Provisional Sinn Féin" has fallen out of use, and the party is now known simply as "Sinn Féin".

Sinn Féin members have been referred to colloquially as "Shinners", a term intended as a pejorative.

Sinn Féin was founded on 28 November 1905, when, at the first annual Convention of the National Council, Arthur Griffith outlined the Sinn Féin policy, "to establish in Ireland's capital a national legislature endowed with the moral authority of the Irish nation". Its initial political platform was both conservative and monarchist, advocating for an Anglo-Irish dual monarchy unified with the British Crown (inspired by the Austro-Hungarian Compromise of 1867). The party contested the 1908 North Leitrim by-election, where it secured 27% of the vote. Thereafter, both support and membership fell. At its 1910 ard fheis (party conference) attendance was poor, and there was difficulty finding members willing to take seats on the executive.

In 1914, Sinn Féin members, including Griffith, joined the anti-Redmond Irish Volunteers, which was referred to by Redmondites and others as the "Sinn Féin Volunteers". Although Griffith himself did not take part in the Easter Rising of 1916, many Sinn Féin members who were members of the Volunteers and the Irish Republican Brotherhood did. Government and newspapers dubbed the Rising "the Sinn Féin Rising". After the Rising, republicans came together under the banner of Sinn Féin, and at the 1917 ard fheis the party committed itself for the first time to the establishment of an Irish Republic. In the 1918 general election, Sinn Féin won 73 of Ireland's 105 seats, and in January 1919, its MPs assembled in Dublin and proclaimed themselves Dáil Éireann, the parliament of Ireland. Sinn Féin candidate Constance Markievicz became the first woman elected to the United Kingdom House of Commons. However, in line with Sinn Féin abstentionist policy, she did not take her seat in the House of Commons.

The party supported the Irish Republican Army during the War of Independence, and members of the Dáil government negotiated the Anglo-Irish Treaty with the British government in 1921. In the Dáil debates that followed, the party divided on the Treaty. The pro-Treaty and anti-Treaty components (led by Michael Collins and Éamon de Valera respectively) managed to agree on a "Coalition Panel" of Sinn Féin candidates to stand in the 1922 general election. After the election, anti-Treaty members walked out of the Dáil, and pro- and anti-Treaty members took opposite sides in the ensuing Civil War.
Pro-Treaty Dáil deputies and other Treaty supporters formed a new party, Cumann na nGaedheal, on 27 April 1923 at a meeting in Dublin, where delegates agreed on a constitution and political programme. Cumann na nGaedheal went on to govern the new Irish Free State for nine years (it merged with two other organisations to form Fine Gael in 1933). Anti-Treaty Sinn Féin members continued to boycott the Dáil. At a special Ard Fheis in March 1926, de Valera proposed that elected members be allowed to take their seats in the Dáil if and whe…

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Sinn Féin is the largest Irish republican political party, and was historically associated with the Irish Republican Army, while also having been associated with the Provisional Irish Republican Army in the party's modern incarnation. The Irish government alleged that senior members of Sinn Féin have held posts on the IRA Army Council. However, the SF leadership has denied these claims.

A republican document of the early 1980s stated: "Both Sinn Féin and the IRA play different but converging roles in the war of national liberation. The Irish Republican Army wages an armed campaign... Sinn Féin maintains the propaganda war and is the public and political voice of the movement". Robert White states at that time Sinn Féin was the junior partner in the relationship with the IRA, and they were separate organisations despite there being some overlapping membership.

Because of the party's links to the Provisional IRA, the U.S. Department of State barred its members along with IRA volunteers from entering the U.S. since the early 1970s in accordance with the Immigration and Nationality Act on the grounds that they were associated with the IRA waging war against a legitimate government.

The British government stated in 2005 that "we had always said all the way through we believed that Sinn Féin and the IRA were inextricably linked and that had obvious implications at leadership level".

The Northern Bank robbery of £26.5 million in Belfast in December 2004 further delayed a political deal in Northern Ireland. The IRA were widely blamed for the robbery, although Sinn Féin denied this and stated that party officials had not known of the robbery nor sanctioned it. Because of the timing of the robbery, it is considered that the plans for the robbery must have been laid whilst Sinn Féin was engaged in talks about a possible peace settlement. This undermined confidence among unionists about the sincerity of republicans towards reaching agreement. In the aftermath of the row over the robbery, a further controversy erupted when, on RTÉ's Questions and Answers programme, the chairman of Sinn Féin, Mitchel McLaughlin, insisted that the IRA's controversial killing of a mother of ten young children, Jean McConville, in the early 1970s though "wrong", was not a crime, as it had taken place in the context of the political conflict. Politicians from the Republic, along with the Irish media, strongly attacked McLaughlin's comments.

On 10 February 2005, the government-appointed Independent Monitoring Commission reported that it firmly supported the PSNI and Garda Síochána assessments that the IRA was responsible for the Northern Bank robbery and that certain senior members of Sinn Féin were also senior members of the IRA and would have had knowledge of and given approval to the carrying out of the robbery. Sinn Féin has argued that the IMC is not independent, and that the inclusion of former Alliance Party leader John Alderdice and a British security head was proof of this. The IMC recommended further financial sanctions against Sinn Féin members of the Northern Ireland Assembly. The British government responded by saying it would ask MPs to vote to withdraw the parliamentary allowances of the four Sinn Féin MPs elected in 2001.

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