EU national leaders will meet in Brussels on Thursday and Friday to discuss some of the biggest issues facing the bloc, including the prospect of a member state leaving for the first time and two countries looking to join.
While cliffhanger negotiations for Britain's Brexit deal should dominate the summit, the crisis in Turkey and Syria and the EU's next seven-year-budget will also take up much of the leaders' time. Here is a rundown on the meeting's main themes.
This is the last summit scheduled before Britain's current date of exit from the union of Oct. 31. The European Commission and Britain have been holding last-ditch talks to clinch a deal that leaders can agree on at the meeting.
The main stumbling block is the border between EU member Ireland and the British province of Northern Ireland: how to prevent it becoming a backdoor into the EU's single market without erecting controls that could undermine the 1998 peace agreement that ended decades of sectarian violence.
Possible results include a framework deal for an orderly Oct. 31 Brexit with legal details agreed upon later, an extra EU summit a couple of days before the Oct. 31 deadline, a further Brexit extension, or possibly no deal at all.
EU Budget For 2021-2027
The EU budget, called the Multiannual Financial Framework (MFF), is an enormous undertaking with the union deciding on its finances for the coming six years - 2021-2027. The biggest issue is how the union will cover the shortfall left by Britain's departure.
Member states have yet to agree how much of individual countries' economies - gross national incomes (GNI) - should be contributed to the EU. Suggestions range from as much as 1.114% to as little as 1.0% of members' GNI.
The leaders will discuss how to make the budget fairer by ending the tradition of rebates, where certain member states have historically received reductions of their contributions to the EU budget.
Also on the budgetary agenda are reforms, investments and measures to mitigate financial shocks in the 19 countries sharing the single currency.
Albania and North Macedonia are next in line to join the EU for what would be the bloc's first enlargement since 2013, when Croatia joined. But not all member states are on board.
At ministerial talks on Tuesday, France stuck to its hard line against membership talks for the Balkan countries, setting up a showdown between French President Emmanuel Macron and fellow EU leaders at the summit.
France says challenges facing the EU - including Brexit; China as a "strategic rival"; security threats posed by Russia; and migration - are already too extensive to admit two more states from a region still scarred by the legacy of 1990s wars and struggling with crime and corruption.
France's stance has raised concerns in Brussels about further delays in an already protracted process that could backfire by spurring Balkan states to cultivate closer ties with Russia and China.
Turkey And Syria
On Monday, EU countries agreed to limit arms exports to Turkey over its offensive in northern Syria, prompting condemnation from Ankara, even as they stopped short of a bloc-wide embargo against a NATO ally.
Turkey was already being scrutinized for its drilling for oil and gas in the east Mediterranean, which has triggered condemnations from several EU states.
EU Climate Targets
The summit will be the scheduled gathering of EU leaders before the United Nation's climate summit in Chile in December. A few member states have not yet signed up to the EU goal of becoming climate neutral by 2050.
Other member states are also pushing for more ambitious goals for 2030 goals relative to 1990, currently set at a 40% reduction of carbon dioxide emissions. The tensions prevented the bloc from taking a leadership role in fighting climate change during the UN summit in September.
Confirmation Of Christine Lagarde And Charles Michel
Christine Lagarde is the nominee to be president of the European Central Bank and Charles Michel, currently Belgian prime minister, is slated to be the next head of the European Council, a role that will see him chair EU summits.
Lagarde, former director of the International Monetary Fund, is due to become the first woman president of the ECB on Nov. 1. Michel is due to assume office on Dec. 1.