At just 264 words, Article 50 of the Lisbon Treaty is pretty thin, but we have a rough idea of how the next two years will pan out.
This is how the Brexit timetable is likely to unfold:
:: APRIL 2017
• In the 'interregnum' before the EU Council meets, both sides will start readying their teams and priorities. The Commission's chief negotiator Michel Barnier and his opposite number at the Council, Didier Seeuws, will coordinate strategies - amid rumours of a turf war between the institutions.
• The UK's logistics team will be pulled together by Oliver Robbins, the Prime Minister's hand-picked sherpa or representative. The main political figure in the negotiations will be Brexit Secretary David Davis.
• EU summit will be held in Brussels on 29 April where the remaining 27 countries will agree on the guidelines - they hope - and give its formal mandate to Mr Barnier.
• Look out for movement on the currency markets at this point: if the UK and the EU seem miles apart - and the atmosphere is poisonous - that may have an impact on sterling.
• Negotiations begin in Brussels. David Davis and Michel Barnier are expected to meet twice a week throughout the process (although that has not been confirmed).
• The first item on the agenda: should any Brexit bill for the UK be sorted before trade talks can begin? Expect a big scrap over this. The UK wants trade talks and a Brexit deal to be discussed at the same time.
• The next item is expected to be the legal status of EU citizens in the UK and vice versa.
• 'Breakout teams' will start to meet around the city to analyse different aspects of the divorce. Make no mistake: hundreds of negotiators are involved on both sides.
• On 4 May, Mrs May's Brexit strategy will get its first major electoral test in the local elections in England, Wales and Scotland.
• On 7 May, a new French president will be elected. If the polls are wrong and the eurosceptic Marine Le Pen does triumph, it could be a serious blow for EU negotiators.
:: SUMMER 2017
• The talks should be settling into a rhythm, but never underestimate the seriousness with which the EU view this Brexit bill, which the Commission puts at €60bn (£51bn).
• If this early part of the negotiation is going badly, expect Tory backbenchers to start agitating. Some of the hardline Brexiteers think we aren't obliged to pay a cent and will urge the Prime Minister to walk away with a hard Brexit.
• My experience of Brussels also suggests there will be leaks-a-plenty from the process. With so many competing interests and countries involved, the friction points won't stay behind closed doors for long.
:: SEPTEMBER 2017
• On 24 September, Angela Merkel will find out whether or not she will remain as German Chancellor.
• If it's former European Parliament president and ardent EU-federalist, Martin Schulz, instead, that could stiffen the EU's sinews. Despite countries carrying equal weight on big EU votes, Germany is still the organisation's silverback.
:: AUTUMN 2017
• We should know by now whether the sides are edging towards a deal on the amount of money the UK might owe the EU for future spending it agreed while an EU member.
• If this is still deadlocked, expect talks about a transitional agreement to kick up a gear, as concern mounts negotiators might be running out of time to agree on other basic details about the split.
:: JANUARY 2018
• In the UK, work will have started on the Great Repeal Bill which would see EU law transposed on to the UK's statute books and repeal the European Communities Act. That would need to be ready to go on Brexit Day, two years after Theresa May pulled the trigger.
:: MAY 2018
• Another electoral test for the UK government in local elections. They won't be the only barometer: there are also presidential elections throughout 2018 in Ireland, Czech Republic and Cyprus as well as potential general elections in Italy, Luxembourg, Malta and Slovenia.
:: SUMMER 2018
• The countdown clock will be ticking loudly now. Although the Article 50 process is exactly two years, the talks will have probably had to conclude before...
:: OCTOBER 2018
• ...that's because the final deal has to be scrutinised by the European Parliament, the European Court of Justice and potentially 38 other regional and national parliaments. EU figures, like Michel Barnier and the Parliament's negotiator Guy Verhofstadt, believe for all of that to happen a draft deal should be readied by October.
• If the EU pre-deadline, deadline has been met and a deal is on the table, then we will know the future relationship - and possible trading relationship - when the UK bids adieu in March 2019.
:: JANUARY 2019
• Three months to Brexit and the pressure will be building to: ratify and construct an implementation "sticking plaster" - or to buy more time.
:: MARCH 2019
• The UK will cease to be a member of the EU two years after the process began - which the Brexit-backers have already named Independence Day. Deal or no deal the country will no longer be subject to its treaties.
• If there is no trade deal, then:
1) The UK could default to World Trade Organisation (WTO) rules, which would then allow the Government to negotiate its trading relations with non-EU countries or
2) A transitional agreement could keep the UK/EU relationship going while sector-by-sector talks continue.
• If there is a deal, then there could be an implementation phase to avoid the feared cliff-edge of too brutal an extraction.
• The UK Parliament would also get a vote on the deal, but it seems to be a "take it or leave it" offer. The implications of a rejection are unclear.
There are a few wildcards too: the UK could withdraw its notification or either side could decide to walk away from the table.