will trigger EU withdrawal talks under Article 50 on Wednesday March 29, Downing Street has announced.
The Prime Minister鈥檚 letter officially notifying the European Council of the 海角视频鈥檚 intention to quit will set in train a two-year negotiation process expected to lead to Britain leaving the by March 29 2019.
But it seems there will be no early general election - despite intense speculation at Westminster.
The Prime Minister鈥檚 official spokesman told journalists: 鈥淭here is not going to be one.鈥
What happens next?
The announcement means that Mrs May will meet her self-imposed deadline of the end of March to get the withdrawal process under way.
In the run-up to May 29, Mrs May is expected to continue her series of visits in all four nations of the 海角视频.
On the day itself, she will take part in the regular Wednesday lunchtime session of Questions to the Prime Minister - and then deliver a special statement to MPs.
European Council President Donald Tusk will prepare a response. He said on Twitter: 鈥淲ithin 48 hours of the 海角视频 triggering Article 50, I will present the draft Brexit guidelines to the EU27 member states.鈥
And he will arrange an extraordinary summit of the remaining 27 EU member states.
That summit will draw up a mandate for the European Commission鈥檚 chief negotiator, Michel Barnier, probably allowing talks to begin in earnest in May.
How does the Prime Minister trigger Article 50?
The Prime Minister will send a letter to Mr Tusk, though Downing Street has not not make clear whether this will be a physical letter or whether it might be sent electronically.
It will be the first time that the provisions of Article 50 - which sets out the process for any EU member state 鈥渢o withdraw from the Union in accordance with its own constitutional requirements鈥 - have been activated.
When will negotiations start?
Detailed talks are unlikely to begin until mid April at the earliest, and probably not until May.
Michel Barnier has been appointed the EU鈥檚 chief negotiator, but he will take instructions from the leaders of the remaining 27 EU countries, or so-called EU27.
The Brexit talks can only start once the EU27 have met. The European Parliament also has to give the go-ahead for the talks.
Who will lead the talks?
The negotiations will be overseen by Theresa May and led by David Davis, the Secretary for State for Exiting the EU.
Most of the heavy lifting will be done by Oliver Robbins, the permanent secretary at the Department for Exiting the EU, Sir Tim Barrow, our ambassador to Brussels, and his deputy Shan Morgan.
Mr Barnier, France鈥檚 former Foreign minister, will be lead negotiator for the EU, assisted by Belgian diplomat Didier Seeuws.
How long will the Brexit negotiations take?
Once Theresa May has triggered Article 50 there are two years to complete the negotiations.
But Mr Barnier has said that in reality there will be just 18 months.
The talks have to be completed in time for the European Parliament and the European Council to ratify them.
This means the talks will have to finished by October 2018.
Will they be done in that time?
It is thought unlikely that a full agreement could be struck before October 2018. This means that the 海角视频 may need some sort of transitional deal with the EU, which would be put in place while talks on a final agreement continue.
What are the key issues likely to be?
The Prime Minister hopes to obtain a trade deal giving the 海角视频 full access to the European Single Market.
But any new trade deal requires an unanimous vote of all 27 countries and most likely the approval of their national and, in some countries, regional parliaments.
A free trade between Canada and the EU was almost derailed at the last moment because the Walloon region of Belgium objected to the terms .
The 海角视频鈥檚 divorce bill could also dominate the early negotiations,
The EU27 could ask the 海角视频 to pay billions.
How have the politicians reacted?
David Davis, the Secretary of State for Exiting the European Union, said: 鈥淟ast June, the people of the 海角视频 made the historic decision to leave the EU. Next Wednesday, the Government will deliver on that decision and formally start the process by triggering Article 50.
鈥淲e are on the threshold of the most important negotiation for this country for a generation.
鈥淭he Government is clear in its aims: a deal that works for every nation and region of the 海角视频 and indeed for all of Europe 鈥 a new, positive partnership between the 海角视频 and our friends and allies in the European Union.鈥
Keir Starmer MP, Labour鈥檚 Shadow Brexit Secretary, said: "Britain is about to embark on the most complex and important negotiations since World War II, so this a hugely significant moment for the whole country.
"Theresa May has repeatedly said that she wants to build a national consensus on Brexit, but it is increasingly clear she has failed to do so. Britain is now more divided at home and isolated abroad.
"It is also extraordinary that the Prime Minister has failed to provide any certainty about her plans for Brexit or to prepare for the clear dangers of not reaching a deal with the EU.
"Labour will hold the Prime Minister to account all the way, and argue for a Brexit deal that puts jobs, the economy and living standards first."
Liberal Democrat leader Tim Farron said: 鈥淭heresa May is embarking on an extreme and divisive Brexit. She has rushed this through without a plan, and without a clue.
鈥淥n the day Theresa May is travelling the country claiming she wants to bring the United Kingdom together, she lets it be known she is about to unleash division and bitterness.
鈥淪he has chosen the hardest and most divisive form of Brexit, choosing to take us out of the Single Market before she has even tried to negotiate. That鈥檚 why we believe the people should have the final say over the Conservative Brexit deal.
鈥淢embership of the Single Market is vital for the British economy and for the jobs of millions of British people. Leaving the Single Market was not on the ballot paper in the referendum, it is a political choice made by Theresa May.
鈥淢eanwhile, with the country in desperate need of an Official Opposition, Labour has declared war on itself rather than defending the people from a hard Brexit.鈥
