Analysis: BBC's Europe correspondent Damian Grammaticas
It's just 10 months since Paris was the scene of multiple terrorist attacks, first the massacre of staff at the satirical magazine Charlie Hebdo and then a hostage-taking at a Jewish supermarket.
What happened in Paris on Friday night is exactly what Europe's security services have long feared, and tried to foil. Simultaneous, rolling attacks, with automatic weapons and suicide bombers in the heart of a major European city, targeting multiple, crowded public locations.
The tactics have been used before, in Mumbai and elsewhere. But how they've come to Europe is one of many questions that will have to be answered.
Were the attackers French citizens? If so, how they were radicalised, armed and organised - was it in France, in Syria, and by whom? Why weren't they detected? Is France, after two major attacks this year, uniquely vulnerable or does the carnage in Paris mean all of Europe faces new threats to our public places and events? And if a Syrian link is proven, will France recoil from that conflict or will it redouble its commitment to the fight against radical groups there?
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http://www.bbc.com/news/world-europe-34814203