What happens next... and what sticking points remain between the EU and the UK?
Time is running out for Boris Johnson who has said a no-deal Brexit would represent a failure on all sides.
What is the problem?
The EU's chief negotiator, Michel Barnier, said they have yet to see any "operational, legally binding solution" to the issue of the Northern Ireland backstop.
European Commission president Jean-Claude Juncker and Taoiseach Leo Varadkar both expressed concern that the return of customs controls threatened the Good Friday Agreement guarantee to maintain an open border with the Republic.
But Mr Johnson has insisted that his Brexit plan is a "fair and reasonable compromise" that all sides can agree on.
Political parties in Northern Ireland, not counting the DUP, have also expressed major concerns.
Is there long left to sort things out?
The UK is scheduled to leave the European Union on October 31 but the EU heads of government summit in Brussels on October 17/18 will be crucial.
What if a deal is not reached?
The UK will leave the customs union and single market, the measures which currently keep trade flowing freely.
The border between Northern Ireland and the Republic will, therefore, become the frontier between the EU and a "third country" outside its rules.
Mr Varadkar has promised to do "everything we can to avoid checks on or near the border" but inspections would take place at ports, airports and businesses.
The UK's no deal planning chief Michael Gove told MPs "we will have no checks at the border and no tariffs" but "we wait to see what Ireland and the EU Commission will decide".
What problems will a no-deal scenario potentially throw up?
There are fears that leaving the EU without a deal in place could hit imports of food and medicine.
Just last week, NHS Wales unveiled a so-called "Brexit Warehouse" to store around 1,000 extra products including medical gloves, needles and dressings at a cost of about £5m.
So will the UK be leaving the EU on October 31?
If you believe Mr Johnson, then it's an emphatic yes.
But the Benn Act - the legislation rushed through Parliament after backbenchers took control of the Commons agenda - requires the Prime Minister to seek a delay to Brexit if MPs have not approved a deal, or agreed to leave the EU without one, by October 19.
Mr Johnson has repeatedly said he will obey the law and meet the Halloween deadline with or without a deal - but he has not been clear about how he intends to do both things.