We now know that Theresa May is planning to trigger Article 50 on Wednesday 29 March. But how? And what happens next?
:: First, a reminder: What is Article 50?
The referendum was the UK's signal that it wants to leave the European Union. Article 50 is the formal notification of the UK's intention to leave - the start of a divorce process which lasts for two years.
The article itself is a short, five-point text, enshrined into EU law as part of the Lisbon Treaty in 2009. Prior to that, there was no process at all for leaving the EU.
The text is vague, brief and open to interpretation. Crucially, it has never been tested before because no member has ever left the EU.
There is no precedent, no pattern to follow and so the process and procedures are unclear.
:: How is Article 50 triggered?
Because of the lack of precedent, the mechanics of triggering it are have only recently been considered by officials in London and Brussels.
The only requirement is that the notification is done in writing to the President of the European Council. It could be as simple as one line and sent in the form of an email.
However, given the gravity of the decision and the symbolism of the moment, it's possible the UK Government will make more of it.
The notification letter may include a reference to the UK government's repeated desire that the EU remains a strong partner for Britain post Brexit.
Maybe they will also use the moment to guarantee, in principle, the rights of EU citizens living in the UK post-Brexit - an olive branch ahead of negotiations?
In terms of delivery, if an email is not deemed to be enough, the notification could be hand delivered to the European Council building in Brussels.
But by whom? Perhaps Britain's Ambassador to the EU, Sir Tim Barrow or the Brexit Secretary, David Davis MP?
:: Is the UK still a member of the EU after Article 50 has been triggered?
Yes. The UK will remain a member of the EU for precisely two years from the day of the triggering.
So, with the triggering of Article 50 on 29 March 2017, if all goes to plan, the UK should cease to be a member of the EU at the end of the day on 29 March 2019.
During that two-year period, the UK is still bound by EU laws and regulations. It is also entitled to near-full membership rights but must also honour its commitments as a member and those include financial.
The only areas in the two-year period where the UK is excluded from EU affairs are when the 27 remaining countries are discussing the UK withdrawal or where they are discussing internal EU business.
:: Once Article 50 has been triggered, is there any turning back?
The Article 50 text does not say whether it is reversible and European Union lawyers have never pronounced on the issue.
There is logic to this; if it became clear that it was reversible it would lose its credibility as a one-way ticket out of the club.
In the end, in the unlikely event that the UK decided it wanted to stay in the EU after all, politics - not law - would determine whether Article 50 could be reversed.
Indeed, in the clearest hint yet that the door will remain open, the president of the European Commission Jean-Claude Juncker said on Friday, 10 March: "The day will come when the British will re-enter the boat, I hope."
:: So negotiations between the UK and the EU will begin as soon as Article 50 is triggered?
Not quite. There's a common assumption that in week one after the triggering, the two negotiators - Michel Barnier for the EU and David Davis MP for the UK - will face off across a table and begin the negotiations for Britain's exit. But it won't work like that for several reasons.
The EU Council President, Donald Tusk, has said that the EU side will issue a formal response and broad guidelines within 48 hours of the triggering of Article 50.
Four weeks later, on Saturday 29 April, an 'extraordinary' EU summit of the 27 remaining members will be held in Brussels at which they will formally issue their negotiating topics and red lines.
Once the EU-27 guidelines have been drawn up, no doubt with an overarching political message, the negotiating mandate will formally be handed to the EU Commission's chosen negotiator, French diplomat Michel Barnier.
Then the negotiations can begin - probably a full eight weeks after Article 50 is triggered.
Mr Barnier already has a team of 30 who work for a new Commission department called 'Task Force 50'. They will lead the EU side of negotiations.
:: Is the EU side united with their negotiating strategy or do different countries have different priorities?
Hitherto, the EU has presented a united front on Brexit, but it will quickly become clear that many of the negotiating topics and red lines are unique to individual countries; things will become more granular, complicated and divided.
It will be up to the European Council's behind-the-scenes Brexit negotiator, Belgian diplomat Didier Seewus, to coordinate with the member countries and try to keep negotiations on track.
Some issues will involve such important and divisive decisions, they'll be well above Mr Barnier's pay-grade - they are likely to be negotiated by the leaders themselves.
Because France and Germany both have elections this year, we don't yet know who'll be leading their negotiating teams. And so in reality, the really serious negotiations won't begin until the end of the year.
:: What if the withdrawal process takes longer than the designated two years?
The exit clock starts the moment Article 50 is triggered. Precisely two years later the UK ceases to be a member of the EU.
In that period, the negotiations for the exit must be concluded.
This is an extremely unrealistic timetable to conclude such complicated negotiations; in reality, because of the time taken at the beginning and end of the process to wind up and wind down the negotiations, the actual time negotiating will probably be 15 months at best.
The two-year Article 50 period can be extended, and the UK continue to be an EU member, but only if all 27 remaining countries agree to it unanimously.
:: Article 50 - the full text
1. Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.
2. A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the union shall negotiate and conclude an agreement with that state, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the union. That agreement shall be negotiated in accordance with Article 218(3) of the Treaty on the Functioning of the European Union. It shall be concluded on behalf of the union by the council, acting by a qualified majority, after obtaining the consent of the European Parliament.
3. The Treaties shall cease to apply to the state in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the member state concerned, unanimously decides to extend this period.
4. For the purposes of paragraphs 2 and 3, the member of the European Council or of the council representing the withdrawing member state shall not participate in the discussions of the European Council or council or in decisions concerning it.
A qualified majority shall be defined in accordance with Article 238(3)(b) of the Treaty on the Functioning of the European Union.
5. If a state which has withdrawn from the union asks to rejoin, its request shall be subject to the procedure referred to in Article 49.