What next for the Schengen Agreement?
The Paris attacks are posing big security questions not just for Paris and France, but the wider European Union as well.
EU interior ministers are due to agree tomorrow/on Friday to tighten checks at the external borders of Europe's passport-free Schengen area, to try to boost security.
What happened in Paris though has also re-ignited the controversy over the merits of free movement within Europe.
The Netherlands, for example, has floated the idea of an additional "mini-Schengen" zone, with passport checks at the borders of several Western European states.
US economist Irwin Stelzer reflects on the concept of a border-less Europe.