The Scottish Parliament has voted in favour of holding a second UK independence referendum.
MSPs voted 69 to 59 to back First Minister Nicola Surgeon to seek permission from the UK Government for a ballot to be held between autumn next year and spring 2019.
Ms Sturgeon's minority Scottish Government won the vote following an extended debate thanks to support from the Scottish Greens.
Prime Minister Theresa May has already said she will block another referendum while the Brexit process takes place, stating "now is not the time".
Holyrood’s vote means Ms Sturgeon now has a mandate to seek permission from Westminster to prepare for a referendum.
The last vote to leave or stay in the UK was in 2014 when Scotland chose to stay as part of the union.
But Ms Sturgeon says the circumstances of staying in the UK have since changed because of Brexit. Scotland voted strongly to remain in the bloc.
Ms Sturgeon said: "It is now the will of Scotland's democratically-elected national Parliament that discussions should begin with the UK Government to enable an independence referendum to be held.
"Today's vote must now be respected. The mandate for a referendum is beyond question, and it would be democratically indefensible - and utterly unsustainable - to attempt to stand in the way of it.
"We will now act on the mandate given to us by Parliament by making a formal approach to the UK Government within the next few days, after Article 50 has been triggered.
"This is, first and foremost, about giving the people of Scotland a choice on this country's future.
"The Prime Minister says that now is not the time for a referendum. I agree with that, which is why I have indicated a timescale no earlier than 18 months from now, when the terms of Brexit are clear - something the PM has now indicated she agrees with."
A UK Government spokeswoman said: "The Prime Minister has been clear that now is not the time for an independence referendum, and we will not be entering into negotiations on the Scottish Government's proposal.
"At this point, all our focus should be on our negotiations with the European Union, making sure we get the right deal for the whole of the UK.
"It would be unfair to the people of Scotland to ask them to make a crucial decision without the necessary information about our future relationship with Europe, or what an independent Scotland would look like.
"We have been joined together as one country for more than 300 years. We've worked together, we've prospered together, we've fought wars together, and we have a bright future. At this crucial time we should be working together, not pulling apart."