Republic of Ireland miss out on automatic qualification
They go into play-offs, Denmark through to Euros
Republic needed win to secure top-two spot in group
If the Republic of Ireland don't qualify tonight they will have the back up chance of taking part in the Nations League final section in March, the same too for Denmark.
If Gibraltar stun Switzerland then an Irish win would take them and the Danes straight through.
Nations League (confirmed teams only)
The four nations in each league meet in one-legged semi-finals on 26 March, with the winners playing in the final on 31 March.
The overall winners of each league will qualify for Euro 2020. That means one of Georgia, North Macedonia, Kosovo and Belarus is guaranteed to be at next summer's Euro 2020.
Image source, Getty ImagesRepublic of Ireland v Denmark (19:45 GMT)
Emlyn Begley
BBC Sport at the Aviva Stadium
A huge cheer from the crowd as John Aldridge predicts a 1-0 win for the Republic. The Oxford (and Liverpool) legend is a guest of honour at the Aviva today.
He scored the goal to take the Irish to the 1990 World Cup, it was the 30th anniversary of that goal against Malta recently.
And now the 1990 Irish World Cup song 'Put Them Under Pressure' is blaring out with a bit of a light show.
The atmosphere is building very nicely right now.
Republic of Ireland v Denmark (19:45 GMT)
Some quotes from Denmark boss Age Hareide, who says: "Our players have respect for Ireland. I have said it myself: the team looks good, they are well organised, they are hard to beat.
"All our players say they don't like to play Ireland, and that means respect when players say that because if you said you love to play Ireland, there would be a difference."
But Denmark and Leicester goalkeeper Kasper Schmeichel appears convinced the visitors will secure automatic qualification.
"For me personally, it would only be my second major tournament, so it's a huge game and a game that we're going to win," said Schmeichel.
Republic of Ireland v Denmark (19:45 GMT)
Denmark's Thomas Delaney, a Borussia Dortmund midfielder who has American heritage, has previously described trying to break down Ireland's defence like "opening a tin of beans with your hands".
"We hate to play Ireland at the moment, we've played them so much recently," added the 28-year-old. "We know each other well, and that goes both ways, so we don't have the upper hand in that regard.
"I don't fear Ireland, but I have a great respect. I know it's going to be a difficult game. It's going to be a great atmosphere and Ireland are a team who play with their hearts on their sleeve. It's cliche but it's going to be a war. They are going to bring everything."
Image source, Getty ImagesRepublic of Ireland v Denmark (19:45 GMT)
Emlyn Begley
BBC Sport at the Aviva Stadium
I saw these as I went to get my media accreditation earlier. Didn’t ask any questions and got straight out of there.
Image source, BBC SportGoals have been in short supply in Republic of Ireland matches in this qualifying campaign, with a maximum of only two goals in any game.
Played seven, scored six, conceded four.
These are their qualifying results...
Will the Republic of Ireland qualify for Euro 2020? Why? Why not?
Lionela Knightley: I can imagine Denmark will hold Republic of Ireland with handball goal as Thierry Henry did ten years ago.
Aleksander Pagels: Am I the only Dane here? Anyway, come on Denmark!
This day 10 years ago was a painful one for Republic of Ireland fans.
With it 1-1 on aggregate and in extra-time in the second leg of the World Cup play-off between France and the Republic in Paris, the Irish were 16 minutes away from penalties.
Then came one of the most blatant handballs ever, from former Arsenal striker Thierry Henry, which led to William Gallas scoring what proved to be winning goal to take France to the 2010 World Cup in South Africa.
"Ten years, is it? Wow. I wish there was VAR then, it would have been a lot easier," said Robbie Keane, who played in that match and is now part of Mick McCarthy's backroom team.
"He was one of the biggest players at the time, Henry, and to do what he did, of course it was disappointing, but you can't dwell too much on the past. You can always tell by players' reactions and when Shay Given ran straight to the linesman, I knew there was something wrong."
Image source, Sky SportsRepublic of Ireland v Denmark (19:45 GMT)
Emlyn Begley
BBC Sport at the Aviva Stadium
I had wondered where all the Irish fans were on my walk from my hotel a bit earlier on.
I found the answer when I got a bit closer to the Aviva Stadium, they were all in the pubs near the ground hours early - in great voice too.
Being the ultimate professional I am, I definitely didn’t go in. Definitely didn’t.
There are also three matches in Group J, but Italy have been flawless, winning their first eight games to secure their qualification a long time ago. They will be joined at Euro 2020 by Finland - the first time they've qualified for a major tournament.
Image source, .Now this is just showing off.
Watch Spain midfielders Rodri and Thiago Alcantara show off their long-range passing skills, incredible control and fantastic ball juggling skills during a training session at Atletico Madrid's Wanda Metropolitano Stadium.
The ball does not touch the ground once! One for all you Sunday League players to try out this weekend.
There are three matches tonight in Group F, but nothing to play for other than pride. Sweden booked their place at Euro 2020 with a 2-0 win in Romania. They will finish second behind Spain, who have won the group.
Image source, .Argentina 0-0 Uruguay
We'll also be bringing you updates from Argentina's friendly with South American rivals Uruguay.
Barcelona teammates Lionel Messi and Luis Suarez both start on opposite sides in Tel Aviv this evening.
The game, which was in danger of being cancelled because of fighting in Israel, has just kicked off.
Image source, Getty ImagesRepublic of Ireland v Denmark (19:45 GMT)
As Emlyn said, these two countries must be sick of the sight of each other.
Tonight is a similar occasion to two years ago when they again faced each other in Dublin with a place at a major competition on the line.
After a goalless draw in Denmark in the first leg of a World Cup play-off, the Republic made a dream start as Shane Duffy gave them a sixth-minute lead.
Then it all fell apart. Tottenham midfielder Christian Eriksen produced a masterclass as he scored a hat-trick in a 5-1 win to take the Danes to Russia 2018.
Image source, Getty ImagesRepublic of Ireland v Denmark (19:45 GMT)
Emlyn Begley
BBC Sport at the Aviva Stadium
So who are in the Republic of Ireland's way tonight?
Only Denmark.
You know Denmark, the team the Irish play every few months - this is their sixth meeting since 2017 (World Cup play-offs, Nations League, Euro 2020 qualifier).
Four draws and one defeat every Irish fan has tried and failed to delete from their memory banks.
Denmark are on a remarkable run too - they have only lost once in their last 34 games - when they had to name futsal and freestyle footballers - because of a dispute with the first-team players.
The manager's reward? Age Hareide is getting the boot after Euro 2020 and being replaced by Kasper Hjulmand.
Will the Republic of Ireland qualify for Euro 2020? Why? Why not?
A simple question for you all tonight...
Will the Republic of Ireland qualify for Euro 2020? Why? Why not?
Tweet us using the hashtag #bbcfootball to have your say.
The Republic of Ireland will qualify for Euro 2020 if they beat Denmark. They would need to win by two clear goals in the unlikely event Switzerland draw with bottom of the table Gibraltar to make a three-way head-to-head situation at the top of the group.
Denmark and Switzerland only need a point each to progress.
The Republic of Ireland will be in next March's play-offs if required.
Image source, .This is the formation Mick McCarthy is set to go with, with Sheffield United striker David McGoldrick, who is yet to score in the Premier League, the focal point of the attack.
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Republic of Ireland v Denmark (19:45 GMT)
Emlyn Begley
BBC Sport at the Aviva Stadium
One of the major topics of debate had been which one of Callum Robinson or Sean Maguire might start out wide to support David McGoldrick for the Republic of Ireland.
The answer was neither as Mick McCarthy packs in five midfielders including James McClean and Alan Browne out wide.
Matt Doherty starts at right-back with Seamus Coleman suspended. Not really a downgrade.
Republic of Ireland: Randolph, Doherty, Coleman, Stevens, Duffy, Hourihane, Hendrick, Whelan, McClean, Browne, McGoldrick.
Substitutes: Kevin Long, Clark, Parrott, Cullen, Byrne, Brady, Robinson, James Collins, O'Hara, Maguire, Travers, Judge.
Denmark are strong as you'd expect, with Christian Eriksen and Kasper Schmeichel starting, as well as Borussia Dortmund's Thomas Delaney in midfield. Chelsea centre-back Andreas Christensen is only listed as a sub however.
Denmark: Schmeichel, Kjaer, Jorgensen, Dalsgaar, Schone, Larsen, Delaney, Eriksen, Poulsen, Cornelius, Braithwaite.
Substitutes: Andersen, Ronnow, Hansen, Dolberg, Hojbjerg, Norgaard, Ankersen, Knudsen, Gytkjaer, Christensen, Skov, Wass.