In Scotland, 46 out of the 59 parliamentary constituencies are marginal seats.
That means a swing of just 5% or less to the party who came second in 2017 will see the incumbent lose.
Here, our special correspondent Bernard Ponsonby looks at ten key sets which could prove decisive on election night.
1. North East Fife
Held by the SNPs Stephen Gethins with a majority of just two, this is the top target for the Liberal Democrats. Polls suggest baseline support for the Lib Dems is higher than in 2017 and they will try and tactically squeeze the large Conservative vote. This looks like the SNPs most vulnerable seat. It will be hard fought and the candidates will probably hope that they do not have to endure the torture of a recount.
2. Perth and North Perthshire
The Tories were just 21 votes behind the SNPs Pete Wishart in 2017. Nationalist poll ratings are high at the moment and they will hope that a Brexit factor will count against the Conservatives and in their favour. The Tories have talked up prospects here for many elections but their ‘one more heave’ strategy has never born fruit.
3. Rutherglen and Hamilton West
Won by the SNP in 2015 but regained by Labour in 2017 this will tell us if there is movement between Labour and the SNP and more critically the direction of travel. If the SNP win it could be a portent of a really bad night for Scottish Labour. If Ged Killen holds the seat party workers will feel encouraged about their chances in other Lanarkshire seats. This could be the first seat to declare.
4. Lanark and Hamilton East
This seat is fascinating because last time around the SNP, Conservatives and Labour were all on approximately a third of the vote. The SNP have a majority of just 266 with the Conservatives in second place having witnessed their vote rise by 16% at the 2017 general election. It could all be about tactical voting here but is the trend to keep the SNP out or to give them a bigger majority? This seat, like Rutherglen and Hamilton West, should declare relatively early and will tell us a lot.
5. Glasgow North East
Can the high-profile Shadow Scotland Office Minister Paul Sweeney see off a challenge from the SNP’s Anne McLaughlin, who held the seat between 2015-17. The majority here is a mere 242 votes. If Labour can hold this they will have high hopes in two other Glasgow seats (South-West and East) where the SNP defend majorities of 60 and 75 respectively. The polls suggest the SNP will hold on and that they will regain Glasgow North East.
The polls suggest that the SNP will take this seat, bringing to an end the short parliamentary career of the Conservative Stephen Kerr, who won last time around with a majority of just 148. The SNP are fielding the MEP Alyn Smith. Tactical voting could be key in a contest where Scottish Labour polled 11,000 votes in 2017.
7. East Dunbartonshire
This is the seat represented by the UK Liberal Democrat Leader Jo Swinson so it comes into the one to watch category. She regained it from the SNP in 2017. This is not a marginal but the swing required by the SNP is just over 5% so they will consider it in play although in reality, given her profile, a loss for Jo Swinson would be a major and unexpected upset.
8. Edinburgh West
The Liberal Democrats have a near 3000 majority here but a swing of just 3% to the SNP will unseat Christine Jardine. Given the SNP is polling well, their seats in the capital should be safe, although the Conservatives haven’t given up in Edinburgh South West where they are trying to finish Joanna Cherry’s Commons career. My hunch is that this could be the one to watch in the capital with tactical voting again playing a part in determining the eventual winner.
Lost by Alex Salmond for the SNP in 2017, his former party need a swing of 2.5% to win it back. If the Tories lose, it could put them under pressure in other north-east seats, particularly Aberdeen South, Moray and Banff and Buchan. The Tories are confident of retaining their north-east powerbase based on the ‘get Brexit done’ mantra which will play better in some constituencies than others.
10. Caithness, Sutherland and Easter Ross
The SNP are talking up their chances in this seat which the Lib Dems won back in 2017. The swing required is 3.3%. The electorate here are fiercely independent, so no party can take a result for granted.