The polls have opened on a historic day for Scotland as voters determine whether the country should remain part of the United Kingdom.
More than three years after Alex Salmond's SNP secured a landslide victory at Holyrood, the long-awaited referendum on independence is finally taking place.
Polling stations opened at 7am and people have until 10pm to cast their ballot, with the result expected to be known by breakfast time tomorrow.
The crucial ballot, which could see the 307-year-old union between Scotland and England brought to an end, is expected to go down to the wire, with polls showing the contest is too close to call.
A YouGov survey for The Sun and The Times and a separate poll by Panelbase both found 52% of Scots will to vote to stay in the union, with 48% favouring independence, when undecided voters are excluded.
But research by Ipsos-Mori for the broadcaster STV suggested the gap could be even closer, indicating 51% of people will vote No to 49% saying Yes.
After a frenetic final day of campaigning from the rival sides yesterday, the turnout is expected to be high, with 4,285,323 people registered to vote, according to the Electoral Commission.
For the first time 16 and 17-year-olds across the country will be able to take part.
The question facing voters is a simple one: Should Scotland be an independent country?
With the momentum in the final weeks of the campaign appearing to be behind the Yes campaign, the leaders of the three main Westminster parties have all pledged to give Scotland more powers if the outcome is No.
But nationalists dismiss this, insisting only a Yes vote will give Scotland the powers it needs.
First Minister Alex Salmond last night closed his campaign at a packed rally in Perth, where he told supporters the referendum is "our opportunity of a lifetime and we must seize it with both hands".
The SNP leader said: ''This opportunity is truly historic. There are men and women all over Scotland looking in the mirror knowing that the moment has come. It's our choice and our opportunity and our time.''
He stressed: ''We are still the underdogs in this campaign, each and every one of us has a job to convince our fellow citizens to vote by majority for a new dawn for Scotland, for that land of prosperity but also of fairness.''
Mr Salmond told how the referendum campaign had ''changed Scotland forever'', bringing confidence and belief to the nation, as well as an ''understanding that by working together Scotland can be a global success story, a beacon of economic growth, a champion of social justice''.
But US president Barack Obama made clear his support for the union in a message on Twitter, saying: "The UK is an extraordinary partner for America and a force for good in an unstable world. I hope it remains strong, robust and united."
Former prime minister Gordon Brown - a leading figure in the No campaign who has been key in securing the fast-tracked pledge for more powers for Holyrood if the result is No - made his own passionate appeal to Scots to vote to stay in the union.
He told a Better Together rally in Glasgow yesterday that the SNP's main aim is to ''break every single constitutional and political link with our neighbours and friends in the United Kingdom''.
Mr Brown insisted: ''We will not have this.''
The Labour MP said that in the referendum "the silent majority will be silent no more".
He told how the UK had fought and won wars together, as well as establishing the National Health Service and the welfare state together.
''We will build the future together,'' he declared
''What we have built together, by sacrificing and sharing, let no narrow nationalism split asunder ever.''
Dear Scotland, the very best of luck to you, no matter which way you vote today. There are pluses and minuses on both sides of the argument, of course. But I'm sorry you were on the receiving end of such an intimidatory campaign from the pro-union camp - and even sorrier that an Irishman and someone of Irish descent took part in it.