The German government says it is cracking down on irregular migration and crime following recent extremist attacks, and plans to extend temporary border controls to all nine of its frontiers next week.
Last month, a deadly knife attack by a Syrian asylum-seeker in Soligen killed three people. The perpetrator claimed to be inspired by the Islamic State group. In June, a knife attack by an Afghan immigrant left a police officer dead and four other people wounded.
The border closures are set to last six months and are threatening to test European unity. Most of Germany's neighbors are fellow members of the European Union, a 27-country bloc based on the principles of free trade and travel. And Germany - the EU's economic motor in the heart of Europe - shares more borders with other countries than any other member state.
The Polish prime minister on Tuesday denounced the closures as "unacceptable" and Austria said it won't accept migrants rejected by Germany.
Here's a look at some of the issues:
