Several European countries reintroduced border controls in response to the surge of migrants and asylum seekers that overwhelmed their systems last year.
The continent's Schengen area allows passport-free travel between 26 countries that have abolished their internal border controls.
But the Schengen rules have provisions for emergencies, allowing participating nations to reinstate border controls in case of "a serious threat to public policy or internal security."
The following five countries are currently using border checks to better control migrant flows. EU governments on Thursday agreed to allow the controls to continue for up to six months.
GERMANY reintroduced controls on September 13, particularly at its border with Austria. Germany became migrants' prime destination after it decided to not turn away Syrian asylum seekers - a decision it later reversed. Berlin has prolonged the controls several times. They are currently valid until May 13, but the government has said that it will extend them until the European Union's outer borders are properly controlled.
AUSTRIA reintroduced controls on September 16, particularly at its borders with Slovenia and Hungary. Austria had been the country that most migrants crossed to reach Germany. Vienna has prolonged the controls several times; they are currently valid until May 16.
SWEDEN reintroduced controls on November 12, particularly at harbours in the south and west, as well as at the Oresund rail and road bridge between Denmark and Sweden. Alongside Germany, Sweden had been one of the migrants' main destinations. Stockholm has prolonged the controls several times; they are currently valid until June 7.
NORWAY reintroduced controls on November 26, particularly at ports with ferry connections to other Schengen countries such as Denmark, Germany and Sweden. Oslo has prolonged the controls several times; it announced Tuesday that it intends to keep them in place until at least June 11. Norway is not an EU state but participates in Schengen.
DENMARK reintroduced controls on January 4, particularly at land crossings and ferry terminals along its frontier with Germany. Copenhagen has prolonged the controls several times; they are currently valid until June 2.
SLOVENIA, HUNGARY and BELGIUM had also reintroduced border controls in September, October and February, respectively, but have since discontinued them.
FRANCE also has controls in place at its land borders and airports, but for security reasons not related to migration.
The other members of Schengen are the Czech Republic, Estonia, Finland, Greece, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Slovakia, Spain and Switzerland.