Nicola Sturgeon has said she wants a second Scottish independence referendum to take place on October 19, 2023.
However, while the first minister has announced plans, their legality still needs to be decided by the Supreme Court.
The first minister said she wanted an "indisputably lawful" referendum to be held, arguing that opponents to Scottish independence would challenge proposals in courts if she did not go to the judiciary herself.
In a letter to Prime Minister Boris Johnson, Ms Sturgeon informed him of the content of today's statement and outlined Scottish government plans to negotiate terms.
Ms Sturgeon said that if the court does refuse proposals, the next general election would become a "de facto referendum".
What happens next?
Currently, Ms Sturgeon's plan is to negotiate terms with the UK government and be granted a Section 30 order - which would increase the Scottish government's legislative powers, enabling them to trigger an independence referendum.
However, the UK government has consistently rebuffed the notion of a Section 30 and so denied Holyrood the ability to hold another Indyref.
Part of the Scotland Act allows Scotland's top lawyer, the Lord Advocate the power to refer to the Supreme Court the question of whether provisions in the draft “Scottish Independence Referendum Bill” relate to reserved matters.
This is a power exercisable solely by the Lord Advocate, not by Scottish Ministers collectively.
The UK government says the constitution is reserved to Westminster, meaning Holyrood cannot organise a vote on its own.
If a referendum was sanctioned, a majority vote would not by itself make Scotland independent.
In the case of a majority vote for independence, legislation would then need to be passed by the UK and Scottish Parliaments.
If the supreme court rules against Ms Sturgeon however, it is likely to put significant pressure on her government, who's main pledge upon election was securing Scottish independence.
To circumvent this, the first minister has announced that if the motion fails to pass, the next general election will also serve as a "de-facto referendum."
What has the reaction from opposition politicians been across the country?
Boris Johnson said he would study Nicola Sturgeon's plans for a second referendum but "the focus of the country should be on building a stronger economy".
"I haven't seen exactly what she's said yet," he told reporters as he travelled to Madrid for the Nato summit.
"We will study it very carefully and we will respond properly.
"The focus of the country should be on building a stronger economy, that's what we're doing with our plan for a stronger economy and I certainly think that we'll be able to have a stronger economy and a stronger country together."
Responding to the plans, Scottish Conservatives leader Douglas Ross accused the SNP of "taking its eye off the ball" and being "selfishly obsessed" with another referendum.
“The real priorities of people across Scotland are on the back burner. Instead, the First Minister is putting her plans to divide Scotland front and centre," he told MSPs.
"She will use government time and resources to further her plan to break up the country, just when we need to be pulling together and working as one."
Mr Ross added: "It will damage efforts to rebuild our country after Covid. It is the last thing a clear majority of Scottish people want."
He also said "we won't take part in a pretend poll" and accused Ms Sturgeon or presiding over a "do-nothing Parliament".
Scottish Labour leader Anas Sarwar said the first minister’s timing was wrong in launching the campaign while the Covid-19 pandemic was still causing people to lose their lives.
He said: “For households across Scotland, it doesn’t feel like this crisis is over.
“Isn’t it the case that the pandemic Nicola that said she wanted us to pull us through is gone, and the partisan Nicola Sturgeon that wants to divide our country is back, pursuing a referendum that two-thirds of Scots don’t want right now.”
Speaking to ITV News, Conservative MP for Aberdeenshire West and Kincardine, Andrew Bowie added: "We simply do not agree to the terms being set out by the first minister.
"It is a gross dereliction of duty that is yet to get legal backing and it feels like a last desperate throw of the dice.
"We have so many issues that we need to sort out such as the cost-of-living crisis, hospital waiting times and the war in Ukraine.
"We will have no part in it, especially if the referendum is found to be illegal, which I believe the Supreme Court will find it to be."
Earlier, Boris Johnson refused to rule out the chance of there being a second referendum, speaking at the G7 summit.
"Our plan for a stronger economy works better when the UK is together than when it is not together," the PM said.
Following the announcement, Downing Street said Mr Johnson continues to believe it is "not the time to be talking about" a second referendum on Scottish independence, while vowing to "carefully study" the Scottish Government's proposal.
A No 10 spokesperson said: "Our position remains unchanged that both ours and the Scottish Government's priority should be working together with a relentless focus on the issues that we know matter to people up and down the country.
"That remains our priority, but a decision has been taken by the first minister, so we will carefully study the details of the proposal and the Supreme Court will now consider whether to accept the Scottish Government's Lord Advocate referral".
Asked whether the prime minister would open negotiations for independence in Scotland if Scots vote for it in a referendum in October 2023, the official said: "We're obviously not going to get into hypotheticals".
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know