Down to business. Earlier this week, the Brexit Secretary, David Davis, agreed the timetable for the talks with his counterpart in Brussels. Today Theresa May heads to the summit with the first set of real proposals that are up for negotiation.
As both sides have suggested, one of their first tasks is to settle the anxieties of the many EU citizens who live in the UK, and the Brits who have made their lives abroad. They have until now been able to do so under rights of freedom of movement that work under European law. For people with families, jobs, businesses, lives, there is an obvious desire to know what happens next, and Theresa May has, unlike her political opponents, refused so far to guarantee anything for EU citizens in the UK until the EU is ready to do the same.
And it is, of course, not just as simple as saying everyone can stay. What services and benefits will they be entitled to? For how long? What about any children they may have in future? What about family in other countries who want to come to the UK after Brexit?
The UK will set out its official position paper on Monday, but tonight Theresa May will outline her "generous offer" to the other EU leaders at the summit dinner tonight. Until we see the black and white of the negotiating document next week we don't know the complete details, but some of the likely clashes are clear.
First of all, neither side is suggesting that people who have already moved to the UK from the EU should have to leave. Government sources suggest they will be able to keep all of their existing entitlements and rights (with possible complications over voting rights although it's not entirely clear).
For the Brussels side, on the principle that EU citizens are all equal under EU law, this is the easy bit to agree. But there is an immediate stumbling block to overcome.
On the EU side, there's a belief that this should apply to any EU citizen who moves to the UK right up until the actual moment of Brexit - for them, until that moment, EU law continues to apply, so anyone who chooses to move in the next 18 months must be treated equally. The British government is not so sure, with suggestions that the moment that Article 50 was triggered in March would be a reasonable starting point for negotiation.
Second, while both sides want to protect their citizens who are already in other EU countries, what about relatives, or children they are yet to have?
Again, on the EU side, rights of family reunification, (bringing in family members from abroad) must be part of the deal, again it's about equality under EU law. And the rights that any EU citizen extends to their family - so in their thinking their children for example would be entitled to free healthcare and education, just as British children are.
But it's not clear yet that the UK government wants to extend its "generosity" in that way. With the desire to cut immigration and tougher rules affecting citizens from other parts of the world, once we are outside the EU do the Spaniards, Poles, Italians, Germans or whoever else remains, keep the rights, not just for them as individuals, but for their families too? There are plenty of hypothetical questions here that aren't clear to answer.
Lastly, as across the EU negotiations, there is likely to be a clash, not just over the rules, but over who enforces them. Time and again Theresa May has said that the European Court ought not to have any say once we leave. It's a huge political priority for her. But for the EU, citizen's rights that were granted under EU law must therefore be policed by EU courts. You can't have a functioning agreement without a deal over who is in charge. Someone will have to budge.
Other aspects of this part of the negotiation will no doubt flare up. Until we see the official negotiating position this is only a taste of the trouble ahead. And government sources do believe the offer they have to put is a good one.
But while the EU and the UK both genuinely want to sort this out, and quickly, both sides know the promises they make might sound easy in theory, but in practice will take compromise to sort out.