Nicola Sturgeon has said she wants a referendum on Scottish independence to take place on 19 October 2023.
The UK Supreme Court is now going to decide if she has the legal powers to press ahead with the vote - with a key case to be heard in October
So is another referendum now inevitable?
Hasn't Scotland already had an independence referendum?
Yes, in September 2014, when Scottish voters were given the choice of staying in the UK or becoming an independent country.
They backed staying the UK by 55% to 45%.
Why is independence back in the spotlight now?
In truth, it has never really gone away.
Ms Sturgeon called for another referendum - "indyref2" - immediately after the UK as a whole voted to leave the EU in the 2016 Brexit referendum. Scottish voters backed remain by 62% by 38%.
Independence supporters argued that Scotland should take its future into its own hands, and no longer be tied to the UK and its Conservative government.
Since then Ms Sturgeon has made repeated attempts to push for another vote but there has been no agreement with the UK government.
Both of the candidates to replace him in Downing Street - Liz Truss and Rishi Sunak - have also opposed a vote.
The SNP currently has a pro-independence majority in the devolved parliament alongside the Scottish Greens. It argues that its electoral success - coupled with the Brexit vote - mean it has a "cast-iron mandate" to hold another referendum.
But the UK government has made clear it has no intention of granting formal consent for a referendum through what is known as a Section 30 order.
This was put in place ahead of the 2014 referendum. Many - but not all - experts believe such a mechanism would be needed again to ensure any vote is legal. Ms Sturgeon wrote to the prime minister saying she wants a similar agreement this time but Boris Johnson said no.
Will indyref2 happen?
The UK government argues that the 2014 referendum was, in Ms Sturgeon's own words at the time, a once-in-a-generation opportunity.
Boris Johnson previously suggested that means another one shouldn't be held for about 40 years.
The UK government has accused the SNP of failing to give clear answers to key questions on issues like currency and pensions in an independent Scotland. It warns any attempt by Scotland to rejoin the EU would lead to a hard border between the two countries.
Ministers also say Ms Sturgeon and her government should be focusing on recovery from the Covid pandemic and improving public services like health and education.
So what is Ms Sturgeon's plan?
The first minister has already started publishing a series of papers setting out the case to break away from the UK.
She has also set out her plans for the way forward without a section 30 order if the UK government's stance doesn't change.
The Scottish government has published a referendum bill which proposes that the vote should take place on 19 October 2023.
Ms Sturgeon said the referendum would be consultative. This means that if there was a yes vote then legislation would have to be passed at both Westminster and Holyrood before Scotland became independent.
The first minister said this meant it would have the same status as the independence vote in 2014 and the Brexit referendum.
Scotland's top law officer, the Lord Advocate, referred the case to the Supreme Court so it can rule on whether MSPs have the power to set up such a referendum without Westminster's backing. The court has set a date to hear the case - October 11 and 12
If the court rules in the Scottish government's favour, Ms Sturgeon said it would move quickly to pass the referendum bill.
If not, the first minister said the next general election would become a "de facto referendum", with the SNP standing on a single issue of independence.
In response, the UK government said it was not the time to be talking about another independence referendum, and that constitutional matters are clearly reserved to Westminster.
Would Scots vote for independence?
According to polling expert Prof Sir John Curtice, the last half dozen polls have - on average - put support for independence at 49%, with 51% against, once "don't know" votes are excluded.
This suggests that the country hasn't seen the big surge in support for independence that Ms Sturgeon hoped for in the wake of Brexit, the Covid pandemic and Boris Johnson becoming prime minister.
But with such a slender lead in the polls, the pro-UK side cannot be confident of victory, and will be mindful of how support for independence increased before the last referendum.
However polling has also suggested that there are fewer undecided voters now than there were at the start of the last referendum campaign, so it may be harder for either side to win people over.