There is a detailed report here on the Paris attacks by ISIS and the logistics/planning that went into the operation.
They have exploited weaknesses in Europe’s border controls to slip in and out undetected, and worked with a high-quality forger in Belgium to acquire false documents.
The scale of the network that supported the attacks, which took 130 lives and wounded 813 people, has also surprised officials, as President François Hollande of France acknowledged on Friday. There are now 20 people in detention in six countries on suspicion of assisting the attackers.
French officials have repeatedly warned citizens that more attacks are possible, saying security and intelligence officials cannot track all the Europeans travelling to and from Islamic State strongholds in Syria and Iraq. And western intelligence officials say their working assumption is that additional Islamic State terrorism networks are already in Europe, with more being formed.
... The documents and interviews with officials show the arc of the Islamic State’s growth from a group that was widely viewed as incapable of carrying out large-scale terror attacks. And they suggest that nearly two years of previous , failed attacks overseen by the leader of the Paris assault, Abdelhamid Abaaoud, served both as test runs and initial shots in a new wave of attacks the Islamic State leaders have called for in western Europe and Britain.
... All the previous attacks by Islamic State fighters dispatched from Syria had relied on a single mode of operation: a shooting, an explosion or an attempted hostage-taking. In Paris, the attackers set off to do all three, realising that this way they could overwhelm the country’s emergency response.
The attacks marked a subtle shift in the Islamic State’s external operations branch, which was first publicised in the group’s French-language online magazine, Daral-Islam, last March. In the previous small-scale attacks, the Islamic State, much like al-Qaeda before it, had taken aim at symbolic targets, including police and military installations and establishments with clear links to Israel or Jewish interests, like the Jewish Museum in Brussels. But in an interview published in the online magazine, a senior operative for the Islamic State, described as the godfather of French jihadis, advised his followers to abandon the symbolism.
“My advice is to stop looking for specific targets. Hit everyone and everything,” he said.
... In the end, it took four elite brigades to stop three gunmen, the report said.
... According to the friend’s account to the police, Abaaoud regaled them with stories about how he had made it to Europe by inserting himself in the stream of migrants fleeing across the Mediterranean. He explained that he was among 90 terrorists who had made it back and who had gone to ground in the French countryside, the friend told the police.