Brexit was not on the initial agenda for the summit but it will be impossible to avoid discussing it, even if the meeting is part of the "Berlin process" launched in 2014, whose long-term aim was to gain more EU members, rather than lose a long-established one.
French President François Hollande, German Chancellor Angela Merkel and Italian Prime Minister Matteo Renzi, who met last week to discuss the consequences of the British leave vote, are to meet the leaders of Macedonia, Bosnia, Kosovo, Serbia, Albania and Montenegro, who are at various stages in the process of joining the EU.
Slovenia, Croatia and Austria, neighbours to the Balkan states who are already EU members, will also be present, as will EU foreign policy chief Federica Mogherini.
Migration, jihadis and the Balkan route
Migration, a key issue in the British referendum, is set to be discussed - the Balkans route is taken by migrants fleeing war in Syria and Iraq and is also the way many aspiring jihadis go to fight in those countries, some returning to carry out attacks in western Europe.
The meeting will discuss investing 400 million euros, 140 million of them coming from the EU, in developing transport and energy infrastructure and setting up a regional office for youth, similar to the already-existing Franco-German youth office.
Business leaders and civil society groups will meet on the sidelines in the morning.