The UK Independence Party (UKIP /ˈjuːkɪp/ ^ⓘ YOO-kip) is a Eurosceptic, far-right populist political party in the United Kingdom. The party reached its greatest level of success in the mid-2010s, when it gained two members of parliament (both through defections) and was the largest party representing the UK in the European Parliament. The party is currently led by Nick Tenconi, the COO of Turning Point UK.

UKIP originated as the Anti-Federalist League, a somewhat single-issue Eurosceptic party established in London by Alan Sked in 1991. It was renamed UKIP in 1993, but its growth remained slow and was largely eclipsed by the Eurosceptic Referendum Party until the latter's 1997 dissolution. In 1997, Sked was ousted by a faction led by Nigel Farage, who became the party's preeminent figure. In 2006, Farage officially became leader and, under his direction, the party adopted a wider policy platform and capitalised on concerns about rising immigration, in particular among the white British working class. This resulted in significant breakthroughs at the 2013 local elections, 2014 European parliamentary elections, and 2015 general election. After the UK voted to leave the EU in the 2016 Brexit referendum, Farage stepped down as UKIP leader, later joining the Brexit Party (now known as Reform UK), which is widely considered to be UKIP's successor. UKIP subsequently saw its vote share and membership heavily decline, losing all of its elected representatives amid much internal instability and a drift toward a far-right, anti-Islam stance.

Ideologically positioned on the far-right of British politics, UKIP is characterised by political scientists as a right-wing populist party. Its primary emphasis has been on hard Euroscepticism; it was one of the first to call for the United Kingdom's exit from the European Union (EU). It promotes a British unionist and British nationalist agenda, encouraging a unitary British identity in opposition to growing Welsh, Irish and Scottish nationalisms. UKIP has also placed emphasis on lowering immigration, rejecting multiculturalism, and opposing what they call the Islamification of Britain. Influenced by Thatcherism and classical liberalism, it describes itself as economically libertarian and promotes liberal economic policies. On social ideals such as LGBT rights, education policy, and criminal justice, it is traditionalist. Having an ideological heritage stemming from the right-wing of the Conservative Party, it has distinguished itself from the political establishment through heavy use of populist rhetoric, for example, through Farage's description of its supporters as the "People's Army".

Governed by its leader and national executive committee, UKIP is divided into 12 regional groups. While gaining electoral support from various sectors of British society, psephologists established that at its height, UKIP's primary voting base consisted of older, working-class white men living in England. UKIP has faced a critical reception from mainstream political parties, much of the media, and anti-fascist groups. Its discourse on immigration and cultural identity generated accusations of racism and xenophobia, both of which it denies.

UKIP began as the Anti-Federalist League, a Eurosceptic political party established in 1991 by the historian Alan Sked. The League opposed the recently signed Maastricht Treaty and sought to sway the governing Conservative Party towards removing the United Kingdom from the European Union (EU). A former Liberal Party candidate, member of the Bruges Group, and professor at the London School of Economics (LSE), Sked had converted to Euroscepticism while teaching the LSE's European Studies programme. Under the Anti-Federalist League's banner, Sked was a candidate for member of parliament (MP) for Bath at the 1992 general election, gaining 0.2% of the vote. At a party meeting held in the LSE on 3 September 1993, the group was renamed the UK Independence Party, deliberately avoiding the term "British" so as to avoid confusion with the far-right British National Party (BNP).

UKIP contested the 1994 European Parliament election with little financing and much infighting, securing itself as the fifth-largest party in that election with 1% of the vote. During this period, UKIP was viewed as a typical single-issue party by commentators, some of whom drew comparisons with the French Poujadist movement. Following the election, UKIP lost much support to the Referendum Party; founded by the multi-millionaire James Goldsmith in 1994, it shared UKIP's Eurosceptic approach but was far better funded. In the 1997 general election, UKIP fielded 194 candidates and secured 0.3% of the national vote; only one of its candidates, Nigel Farage in Salisbury, secured over 5% of the vote and had his deposit returned. UKIP was beaten by the Referendum Party in 163 of the 165 seats in which they stood against each other. The Referendum Party disbanded following Goldsmith's death later that year, and many of its candidates joined UKIP.

After the election, Sked was pressured into resigning by a party faction led by Farage, David Lott and Michael Holmes, who deemed him too intellectual and dictatorial. Sked left the party, alleging that it had been infiltrated by racist and far-right elements, including BNP spies. This connection was emphasised in the press, particularly when Farage was photographed meeting with BNP activists. Holmes took over as party leader, and in the 1999 European Parliament elections—the first British election for the European Parliament to use proportional representation—UKIP received 6.5% of the vote and three seats, in South East England (Farage), South West England (Holmes), and the East of England (Jeffrey Titford).

An internal power struggle ensued between Holmes and the party's national executive committee (NEC), which was critical of Holmes after he called for the European Parliament to have greater powers over the European Commission. Led by Farage, the NEC removed Holmes from power, and Titford was elected leader. In the 2001 general election, UKIP secured 1.5% of the vote, and six of its 428 candidates retained their deposits. It had lost much of its support to the Conservatives, whose leader William Hague had adopted increasingly Eurosceptic rhetoric during his campaign. In 2002, the former Conservative MP Roger Knapman was elected UKIP leader, bringing with him the experience of mainstream politics that the party had lacked. Knapman hired the political campaign consultant Dick Morris to advise UKIP. The party adopted the slogan "say no" and launched a national billboard campaign. In 2004, UKIP reorganised itself nationally as a private company limited by guarantee.