The European Commission, the European Union's executive, will on Wednesday propose reforms to the way the bloc admits new members in an attempt to convince French President Emmanuel Macron to lift his veto on membership negotiations.
Here are some facts about the six Balkan aspirants:
The European Commission has recommended that Albania, already a member of NATO, formally start membership negotiations, but Tirana still needs approval from the EU's 27 governments to begin talks, which once underway could still take many years.
At war from 1992 to 1995, Bosnia is still overseen by EU-led peacekeepers. It submitted an EU membership application in 2016, which is pending approval. That means it is not yet a candidate country although it is seen as a potential one.
Kosovo, which declared independence from Serbia in 2008, wants to join the EU but is far from being able to do so. It must mend ties with Serbia through EU-mediated talks, being restarted by new EU foreign policy chief Josep Borrell. Five EU countries do not recognise Kosovo's independence: Slovakia, Spain, Greece, Cyprus and Romania.
North Macedonia, like Albania, is an official candidate for EU membership and needs EU government approval to start negotiations. Its prospects were greatly improved after it overcame a decades-long dispute with neighbouring Greece over its name, agreeing to be called the Republic of North Macedonia. It is set to join NATO in 2020.
Montenegro, which joined NATO in 2017, is already in negotiations to join the EU and is seen by the European Commission as likely to join the bloc later this decade, along with Serbia.
The largest Balkan country with 7 million people, Serbia is also in the midst of negotiations for membership. It is seen as the lynchpin in the region and the EU hopes Belgrade's influence in the Balkans could help others reform. In February 2018, the Commission said Serbia could join the EU by 2025, albeit saying that was very ambitious.