Note to readers: Luna17 will be live-blogging commentary on the results as they are announced, starting around 11pm tonight. I'll be reporting, and commenting on, the big stories in mainstream politics and also the fortunes of left-wing candidates.
This is the first historically significant UK general election since 1997 and the Labour landslide which swept away 18 years of Tory government. We have ahead of us the first genuinely unpredictable election night since 1992, when John Major's Tories upset the predictions of a Labour victory.
This, in fact, is the first time since Margaret Thatcher's ascendancy in 1979 that a general election has been both highly significant and unpredictable. It is politically important and likely to be dramatic.
The last two elections - in 2001 and 2005 - largely reaffirmed the status quo, and the results were never in much doubt. Of course, the Tories had already made some advance on Labour by 2005, but it still came out of that election a long way behind in seats won (though the relative narrowness in the popular vote was noteworthy).
At times since David Cameron became the party's leader the Tories have commanded whopping leads in the polls. For a long time it looked inevitable that the next election, when it eventually came, was set to deliver a comfortable Tory majority - on the back of long-term mass disillusionment with New Labour combined with newfound credibility for the Tories. But that has changed.
By the start of this election campaign things looked less secure for Cameron's Tories, yet it still seemed there was a good chance of at least a slim majority. The growth of the Lib Dems' support has put the Tories in a far more vulnerable position - a majority government for them now seems highly unlikely. A hung parliament - for the first time since 1974 - is probable.
Nobody predicted the Lib Dems' success in this campaign. It was the first (of three) televised leaders' debates that lifted Nick Clegg from also-ran to serious contender. It still isn't clear if the Lib Dem surge has been entirely sustained, but the first leaders' debate decisively took the party to a higher level. Today might even represent the permanent end of the old Tory-Labour dominance, but this is still far from certain.
Clegg's success rests upon a simple combination of two factors. The BBC's Nick Robinson noted, at one stage of the campaign, that a poll found 75% of people want a change from Labour but only around 35% thought the Tories represented that change. There's quite a gap between those two figures - and into that gap steps Nick Clegg, presenting his party as an alternative to the 'old politics' symbolised by the MPs' expenses scandal.
In truth the Lib Dems are a minor variation on the same theme. Most importantly, all three parties are committed to drastic public sector cuts, which are likely to be more severe than the parties have publicly revealed.
A Financial Times editorial at the weekend declared: “Whichever party wins this election will need to sack public sector staff, cut their wages, slash benefits, reduce pensions and axe services. None, however, has deigned to explain that.”
Voters “are in for the shock of their lives – and will respond with fury when they learn the truth... Their anger, moreover, will not be directed at bankers or bureaucrats. It will be aimed at the politicians who hid their plans from the public.”
Indeed in Greece we're seeing protestors direct their anger primarily at the politicans, highlighting the acutely political character of the crisis and of responses to it. There could be a storm brewing here too. What happens tonight will impact hugely on the politcal context in which cuts will be imposed and resistance mounted.
Follow my live-blogging from 11pm tonight.