MSPs have backed Nicola Sturgeon's calls for a second independence referendum in Scotland.
The Scottish Parliament voted 69 to 59 in favour of the First Minister's plan to seek permission from the UK Government for a vote to be held between autumn next year and spring 2019.
Ms Sturgeon's minority government won the vote with help from the Scottish Greens.
After the vote, Ms Sturgeon said the referendum would be "first and foremost, about giving the people of Scotland a choice on this country's future".
A UK Government spokeswoman echoed this, saying they would "not be entering into negotiations on the Scottish Government's proposal".
She added: "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."
But Ms Sturgeon said the MSPs' vote "must now be respected".
She added: "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."
Sky's Scotland correspondent James Matthews said there were cheers from inside Holyrood and from a small crowd of independence supporters stationed outside the building as the result of the vote was announced.
He added: "The problem for Nicola Sturgeon is that (independence supporters) don't number more than 50% of the Scottish population, according to the opinion polls.
"There is still a firm majority in favour of sustaining or retaining the union and that is her challenge now - to turn over that deficit in public support."
Ms Sturgeon will now write a letter to Mrs May "later this week" with her Section 30 request, a delay that Matthews said was likely due to "politics and PR".
"I think in terms of PR in political campaigning, that letter would have been lost in the coverage and fuss surrounding the triggering of Article 50," he said.
Scottish Conservative leader Ruth Davidson said the decision to go ahead with another vote was "deeply regrettable", while Scottish Labour leader Kezia Dugdale said there was no evidence that Scots want another referendum.
She said: "We have no idea what Brexit looks like, or how it will impact our economy and families in Scotland."
Ross Greer, the Scottish Greens' external affairs spokesman, said: "It should be our responsibility, as those elected by the people of Scotland, to fight for their right to choose their own future."