Voters are going to the polls in the third general election in the UK in under five years - and the fourth in under a decade.
After a six-week campaign, the nation will decide whether the Conservative Party's Boris Johnson or Labour's Jeremy Corbyn will form a government for up to five years.
A total of 650 parliamentary constituencies are being contested in England, Scotland, Wales and Northern Ireland, with polling stations open from 7am until 10pm.
The total electorate is around 46 million and there will be 40,000 polling stations. Unusual locations include several pubs, a hair salon, a laundrette, a chip shop and a windmill.
When all the votes are counted after the polls close, a party needs 326 seats for a majority in the Commons without relying on support from smaller parties.
It is the first December general election since 1923 and the first winter election since February 1974, when Edward Heath and the Conservatives were defeated by Harold Wilson's Labour Party.
Of the last three general elections, in 2010, 2015 and 2017, only one - when David Cameron triumphed in 2015 - has produced a clear-cut winner with one party securing an overall Commons majority.
In 2010, after the Conservatives fell short of a majority, Mr Cameron went into a coalition with Nick Clegg's Liberal Democrats.
And in 2017, after the second hung parliament in seven years, Theresa May was forced to do a deal with Northern Ireland's Democratic Unionist Party (DUP) to keep the Tories in power.
After leading in the opinion polls throughout the 2017 campaign, the final results saw the Conservatives win 318 seats, losing 13. Labour won 262, gaining 30.
The SNP's tally fell from 56 to 35 and the Liberal Democrats were up from eight to 12. Turnout was 68.7%.
The Conservatives are fighting 635 seats, Labour 631, the Liberal Democrats 611, the SNP all 59 in Scotland, Plaid Cymru 36 in Wales, the Green Party 474 and Nigel Farage's Brexit Party 276, having withdrawn from all the seats currently held by the Conservatives.
As ever, this election has been dominated by the party leaders. While Mr Johnson and the Lib Dems' Jo Swinson, who, like the PM, became party leader in July, are fighting their first campaign leading their party, it is Mr Corbyn's second as Labour leader.
He is the first Labour leader to fight more than one election as leader since Tony Blair, who won in 1997, 2001 and 2005, and the first since Neil Kinnock to fight a second campaign after an election defeat.
And what of the weather for this first winter election for almost a century?
The forecast for polling day is unsettled, with prolonged rain for many, according to Sky News weather producer Chris England.
"Thursday morning will bring cloud and outbreaks of rain to most, and snow to northern hills, but Scotland and eastern England will be mainly dry and bright," he says.
"There will be just the odd shower there.
"Most places will be rather chilly again, but it will turn milder in the southwest.
"Southern and central Scotland will turn wet during the afternoon, while Wales and southwestern parts of both Britain and Ireland will see rain giving way to more scattered blustery showers. Most other places will be wet into the evening."
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