On Thursday, leaders are expected to endorse a plan that could involve spending 5.5 billion euros a year, or about $5.7 billion, to help governments bolster their military capacities. But countries including Britain, Lithuania and Poland are wary of any steps that duplicate the work of NATO. Other countries are also skeptical. Ireland, for example, is committed by its Constitution to military neutrality, and Cyprus is leery of Turkey, a NATO member that has occupied the northern half of the island since 1974.

Are membership talks with Turkey over?

The talks were supposed to get a new start under the terms of a deal this year for Turkey to help the European Union to manage the influx of migrants, many from Syria. The talks have been at a standstill since a failed military coup in Turkey in July, which set off a ferocious crackdown against soldiers, civil servants, police officers, judges and other groups. Austria and the European Parliament want a formal freeze to the negotiations. Leaders preserved on Thursday a formal commitment to keep talking with Turkey, even if not much of substance is achieved.

That is likely to include a summit between President Recep Tayyip Erdogan of Turkey and top European Union officials sometime after March.

What about migrants?

Although Turkey has helped clamp down on the flow of migrants entering the European Union via Greece, many desperate people, mainly Africans, are turning to boats crossing the Mediterranean Sea to reach Italy. To reduce deaths at sea and deal a blow to smugglers, European leaders agreed on Thursday to support a nascent European Border and Coast Guard and to continue support for the Libyan Coast Guard. Leaders also agreed to seek ways to expand a system of granting aid to countries outside the bloc in return for their agreement to take back migrants; similar deals are in place with Ethiopia, Mali, Niger, Nigeria and Senegal.

And ‘Brexit’?

The British government is expected to start the formal process for leaving the European Union before the end of March. The process is supposed to take two years, but it could drag on much longer. With anti-European politicians in France and the Netherlands riding high in the polls ahead of elections in those countries in 2017, fears that the bloc might unravel are widespread.

Theresa May, the British prime minister, left the summit meeting on Thursday night to allow the remaining 27 leaders to discuss, over dinner, their strategy for staying united. They also completed their first order of business: agreeing to allow the European Commission, the bloc’s executive body, to lead the negotiations once Mrs. May formally starts the exit process. That puts Michel Barnier, a former French foreign minister and European commissioner, effectively in charge of the talks with London. To placate concerns among some member states that Mr. Barnier will be too inflexible, the leaders also agreed to a structure to monitor those discussions.

Might Greece leave the bloc, too?

Not likely. It is — once again — in open conflict with creditors, who refused on Wednesday to grant the country some modest relief on its towering debt. That could be part of a looming economic crisis for the bloc, which is already contending with the shaky state of Italy’s banks. But there is little sense of panic about a possible departure from the eurozone, as there was 18 months ago.