The European Union is dealing with an increase in legal and illegal migrant arrivals, spurring some member countries to temporarily reintroduce border checks within what is normally a wide area of free movement - the Schengen zone.
Schengen's rules allow this "as a last resort" to avert serious threats to internal security or public policy.
These countries have reinstated or toughened checks:
Austria has checks at its border with the Czech Republic, expiring on April 16; with Slovenia and Hungary until May; and with Slovakia until June 2.
It has cited pressure on the asylum reception system, as well as concerns about weapons and people smuggling and criminal networks linked to the war in Ukraine.
Denmark is carrying out checks on land and sea transit from Germany until May, according to an EU commission report.
France cited threats of terrorism in reintroducing checks on its borders with Schengen countries, to last until April 30.
Germany has established checks on its land frontiers with Poland, the Czech Republic and Switzerland until June 15, citing a surge in migration and smuggling.
Land border checks with Austria are in place until May, with Germany citing strains on its asylum reception system, security threats linked to the Middle East, and the war in Ukraine.
Additionally, Berlin said it will introduce temporary border controls as part of ramped-up security around soccer's 2024 European Championship, starting June 14.
Italy's checks at the border with Slovenia are due to last until June, after Rome said migrants arriving via the Balkans could be terrorists.
Norway, which is not an EU member but belongs to the Schengen arrangement, has reinstated border controls in ports with ferry connections to the Schengen area until May, citing threats to its infrastructure and from foreign intelligence services.
Slovenia has installed border checks with Croatia and Hungary until June, citing a deteriorating security situation in the Middle East and Ukraine, a high threat of terrorism, and organised crime in the Western Balkans.
Sweden has toughened its border checks until May, saying it has thwarted attacks since Koran burnings drew threats from Daesh militants.
Finland has closed crossing stations on its land border with Russia - not a Schengen state - for an indefinite period in response to a surge of asylum seekers from third countries that it said had been orchestrated by Moscow. The Kremlin denied the allegation.
Helsinki also added several ports to a list where travel from its eastern neighbour is prohibited.
