David Cameron has urged MPs to back him over military intervention in Syria against so-called Islamic State extremists.
The prime minister has set out what he called a "comprehensive case" before taking questions from 103 MPs over two hours and 40 minutes during a statement in the Commons.
He set out his response to the Commons Foreign Affairs Committee, which had warned the government against pressing ahead with air strikes.
MPs rejected air strikes against Syrian government targets in 2013. This time around, the PM said there would not be a Commons vote unless there was a clear majority for action, saying a government defeat would "hand a publicity coup" to the IS group.
Following the Paris attacks in November, some MPs' minds are said to have changed and Mr Cameron has called a debate and vote for Wednesday - so where do the parties stand?
The Conservative Party
The majority of Conservative MPs would vote to back extending UK air strikes against Islamic State targets in Syria.
Thirty Conservative MPs rebelled against David Cameron in August 2013, when the Commons rejected his first attempt to launch bombing raids on Syria - albeit against the Assad regime rather than IS militants.
A number of MPs who defied their party then - including Charles Walker and Andrew Bridgen - now say they will support the government, Mr Walker suggesting there was "no room for delay" in taking the fight to the extremists.
One of the 2013 rebels told the BBC they predicted about 15 Conservatives would still oppose any kind of intervention, arguing that bombing could be open-ended and will not help achieve a political solution to the civil war in Syria.
Tory MP Julian Lewis - who chairs the Commons Defence Select Committee - told the BBC the IS group could not be defeated militarily unless Western powers worked with the Syrian regime.
Total number of Conservative MPs: 331
The Labour Party
Labour is split on Syria. Party leader Jeremy Corbyn, until recently chairman of the Stop the War Coalition, has written to all of his MPs saying he does not back Mr Cameron's case for air strikes.
With at least half of his shadow cabinet believed to be in favour of intervention, this letter generated an angry reaction from some on his front bench, with one member warning of resignations if Mr Corbyn tried to impose his view on the party when it comes to the vote.
The party leadership also asked for people to email their views on Syria bombing and claimed that 75% of the 100,000 who responded opposed the bombing.
After what was apparently a stormy shadow cabinet meeting on Monday, the Labour leader has offered a free vote on the issue - which means his MPs won't be instructed to vote in a certain way. BBC political editor Laura Kuenssberg said that, as of Tuesday, around 50 Labour MPs had indicated they were likely to vote for Syria bombing.
Total number of Labour MPs: 231
The Scottish National Party
The SNP, which opposed military action in 2013, has vastly increased its Westminster presence since the general election and can exert real influence.
SNP leader Nicola Sturgeon has said her party will vote against airstrikes, the decision having been taken after a careful assessment of the options.
She said while David Cameron had made progress in convincing sceptics, the SNP still had two main concerns - the lack of reliable ground troops and the need for post-conflict reconstruction in Syria.
Ms Sturgeon said there was an "honest difference of opinion" with the prime minister.
Angus Robertson, the SNP's Westminster leader, has also said there was no effective ground support in place to take and hold territory.
And he said there was no fully-costed reconstruction plan in place for Syria.
Total number of SNP MPs: 54
The Liberal Democrats
Lib Dem leader Tim Farron has written to party members setting out his reasons for backing the government's stance.
He told them in the letter that "the threat to Britain and our allies is clear" and that "we can and must play a part to extinguish Isil".
Mr Farron has also said: "I've made it very clear that our position will be, on balance and in many ways reluctantly, to back the government - because on balance it's a much bigger risk to not act that it is even to act. And I hope that my fellow members of parliament in the Liberal Democrats will join me."
He said that he had been affected by visiting refugee camps on Greek islands and at Calais.
"I can't in all conscience, personally, look at that situation, having met those people in those camps and not act when I could have done," he added.
Total number of Lib Dem MPs: 8
The Democratic Unionist Party
The Democratic Unionist Party, along with the SDLP and the UUP, helped to sink David Cameron's last attempt to launch air strikes in Syria, with five of its MPs voting against the move and three absent.
But DUP Westminster leader Nigel Dodds has now said that the party would support the government's motion.
He said there had been "much discussion" with the prime minister and others in government and that his party had "concluded that the time is right for us to act, and to act decisively".
Mr Dodds added: "Terrorism requires an answer from all civilised countries. We in Northern Ireland know what it's like for terrorism to be ignored or appeased."
Total number of DUP MPs: 8
Voted against military action last time and would be expected to do so again. Party leader Leanne Wood said her party would "listen very carefully" to Mr Cameron's case for air strikes. During the Commons debate, the party's Westminster leader Hywel Williams said all other options should be considered before MPs are asked to vote on military action,
Total number of Plaid Cymru MPs: 3
UK Independence Party
UKIP's MP Douglas Carswell voted with the government in 2013, when he was a Conservative MP, despite expressing reservations about its lack of a "coherent strategy" in Syria. But UKIP has been consistent in its opposition to further military action.
The Green Party's only MP Caroline Lucas has confirmed she will vote against military action in Syria on the evidence presented so far, describing the case presented by Mr Cameron as "neither comprehensive nor compelling".
Social Democratic and Labour Party (SDLP)
The party's MPs voted against military intervention in 2013 and have again expressed reservations.
Total number of SDLP MPs: 3
The party's two MPs have met Prime Minister David Cameron to discuss his plan for air strikes and have said any action should be "thought out" and "targeted" with a clear exit strategy.