Turkey has sought to join the European Union for almost 30 years, but progress has been slow, most recently due to tensions with Cyprus and concerns over Ankara's democratic and human rights record.
But the EU is now looking at speeding up the process in return for Turkish help in stemming migration flows to Europe.
Ankara applied to join the bloc in 1987 and was declared eligible 10 years later. A screening process began in 2005, and in 2006 the EU opened the first of 35 negotiation chapters - policy areas in which candidate countries must bring their rules in line with EU standards.
An overall 15 chapters have now been opened, and one of those, on science and research, has been provisionally closed. The 15th chapter - on economic and financial issues - was opened in December, as part of the EU's bid to enlist Ankara's help in tackling the migration crisis.
Preparations are under way to open five further chapters: on energy policy; the judiciary and fundamental rights; justice, freedom and security; education and culture; and foreign, security and defence policy.
However, the EU has pledged not to open eight negotiation chapters until Turkey grants Cyprus the same treatment it offers all 27 other EU member states. Ankara does not recognize Cyprus' independence.
The blocked chapters include key issues such as external relations, agriculture and the free movement of goods and financial services.
Cyprus has been divided since 1974, when a Turkish invasion resulted in the northern section of Cyprus seceding from the rest of the country and forming the Turkish Republic of Northern Cyprus, which is only recognized internationally by Turkey.
On Tuesday, Cypriot President Nicos Anastasiades said his country would block the opening of further negotiation chapters until Turkey complies with obligations it has entered into with the EU. Peace talks between the two parts of the island are at a critical stage.
Turkey and the EU are in separate negotiations to remove visa requirements for citizens visiting one another's territories. This could also be sped up under the EU-Turkey migration plan, although EU officials have insisted that requirements will not be lowered.
Ankara has so far met 35 of the 72 benchmarks set by Brussels for the liberalization of vizas, according to the European Commission.
Turkey, which has a population of almost 80 million, wants the EU to lift visa requirements for its citizens by the end of June. Many have questioned, however, whether the country would be able to undertake the required measures in time.