The leaders of Greece, Bulgaria, Romania and Serbia gather in Thessaloniki, northern Greece, on Wednesday for the fourth Quadrilateral Summit.
The prospects of the Western Balkans joining the European Union and other regional issues are expected to top the agenda, after the EU decided last month to start accession talks with the Former Yugoslav Republic of Macedonia (FYROM) and Albania.
Prime ministers Alexis Tsipras of Greece, Boyko Borissov of Bulgaria, and Viorica Dancila of Romania, and Serbia's President Aleksandar Vucic, will also be discussing closer cooperation in energy, transport, infrastructure and security.
The refugee crisis is also expected to be a topic of discussion following last week’s EU summit on the issue.
The Thessaloniki meeting is seen as an effort to coordinate the four countries’ positions on a number of key issues ahead of a meeting of the leaders of China and the countries of Eastern Europe and the Balkans in Sofia on Saturday and the Western Balkans Summit of the Berlin Process, which will be held in London next week.
It is the fourth such meeting between the leaders of the four countries and is expected to become a fixture on their diplomatic agendas in light of major recent developments in the region, particularly the name deal between Greece and FYROM, and the EU-Western Balkans Summit that was held in Varna in Bulgaria in May.
The meeting is also expected to help push a number of major infrastructure projects in the region, including the construction of the Gas Interconnector Greece - Bulgaria (IGB) pipeline.
The summit will begin at 6 p.m. with a meeting of the four leaders and a separate meeting of the respective infrastructure and transport ministers.
At 7 p.m., the meeting will include the delegations, and will be followed by a working dinner and a joint press conference at 8.15 p.m.