British Prime Minister Theresa May is looking for compromise from the European Union (EU) in order to move Brexit talks on to the second phase, dealing with future trade arrangements.
So how is the process likely to pan out if she gets her way - and if she does not?
October 9 - Some 473 days since the UK voted for Brexit in the referendum, and 194 since it notified Brussels of its intention to quit under Article 50 of the EU Treaties, the fifth round of withdrawal talks begin in Brussels. The talks are expected to be the last formal negotiations before a crunch summit on October 19 and 20.
Meanwhile, in London Mrs May tells the House of Commons that, after her Florence speech, the ball is now in the EU's court to move the process forward.
October 12 - The latest round of Brexit talks concludes with a press conference by the European Commission's chief negotiator Michel Barnier and Brexit Secretary David Davis. Mr Barnier's comments will be closely scrutinised for hints of whether he will advise EU leaders that "sufficient progress" has been made on the divorce deal to be able to move on to trade.
October 19-20 - Mr Barnier reports back to the EU27 ahead of a two-day European Council summit attended by Theresa May in Brussels. Mrs May will be outside the room when the other 27 leaders make the vital decision on whether "sufficient progress" has been made on the issues of citizens' rights, the Irish border and the UK's "divorce bill". If they decide it has not, then the start of talks on post- Brexit trade arrangements will be delayed until December at the earliest, in a significant setback for the Prime Minister.
November and December - At least two more rounds of formal negotiations are expected. If the European Council has given the green light for talks to move onto the second phase, these will focus on trade relations after Brexit. If not, they will offer a last-ditch opportunity to break the deadlock before Christmas. Britain will also be pressing for agreement on transitional arrangements to avoid a "cliff-edge" Brexit.
December 14-15 - A scheduled two-day European Council summit offers a second opportunity for the EU27 leaders to decide whether talks can move on to trade. Failure to do so would mean crisis for Theresa May, with escalating calls for her to prepare to quit the EU without a deal.
Figures in the City have warned that firms will start moving staff and functions out of the UK if it is not clear by Christmas what transitional arrangements will be in place.
Winter/spring - If talks are proceeding to plan, negotiators can be expected to be getting into the nitty-gritty on how future trade relations will work while ironing out final details of the divorce deal.
March 22-23 - European Council summit in Brussels. If talks have not moved on to the second phase by now, the process will be in serious crisis, with time running out for any discussion of trade and companies across the UK forced to plan for the possibility that there will be no deal. Mrs May will come under pressure to pull out of talks.
May - English local government elections will provide the Prime Minister with her first widespread electoral test since the disastrous snap election of June 8 2017.
October - Mr Barnier hopes to be able to conclude withdrawal negotiations around this point in order to allow time for them to be ratified before the end of the two-year Article 50 deadline.
Winter/spring - The European Court of Justice could be asked to rule on whether the deal requires approval by each EU state. If so, it could have to be ratified by up to 38 national and regional parliaments, with any of them effectively holding a veto.
Mrs May has promised MPs a "take it or leave it" vote on any deal. MEPs in the European Parliament will have the final vote on any agreement.
March 29 - Two years after the invocation of Article 50, the UK ceases to be a member of the EU and is no longer subject to its treaties, whether or not a withdrawal agreement has been reached. Because the exact moment of exit is midnight Brussels time, the UK is due to leave at 11pm on March 29.
The UK Government has made clear it wants an "implementation period" lasting around two years from this point, during which the authorities and businesses can make practical preparations for departure. Ministers insist this period is not intended for further negotiations as the shape of a future trade deal should be known by this point.
June - European Parliament elections will take place without the UK.