This conclusion presents some closing thoughts on the key concepts discussed in the preceding chapters of this book. The book examines the role of innovation and learning of al-Qaeda-inspired terrorist plots and attacks in Europe since the 9/11 attacks in 2001 in order to contribute with an enhanced insight into indicators of innovative behaviour. It illustrates that Brian Jenkins' statement in 1985 still holds true for today's terrorists as their tactical repertoire has changed little over time. The book focuses on indicative of the seeming lack of ability to invigorate terrorist tradecraft in pace with the Western states' dynamic levels of vulnerabilities and critical dependencies. It provides some interesting emerging themes for further investigation as the al-Qaeda phenomenon increasingly become fragmented, the spread of the ideology of al-Qaeda's brand of nihilistic extremism, and the regional wars in Syria and Iraq involving the Islamic State as well as the specter of foreign fighters.