Terrorism has been one of the most important threats to peace, security and stability in many parts of the world. But what does this mean? What is the nature of this threat? What can be done about it and how can we at least limit the impact of terrorism?These are just a handful of questions that will be addressed in this book that consists of four parts. First it focuses on the essence of terrorism as an instrument to achieve certain goals and the difficulties in defining the term. The second part provides an overview of the state of the art of terrorism studies. The most interesting results of this academic field are examined and compared with empirical evidence with the aim to either stress their importance or to debunk them as myths. The final part looks into the impact of terrorism, recent developments and their implications for both academics and policymakers.Edwin Bakker is professor in terrorism studies at Leiden University and works for the Netherlands Police Academy. His research interests include jihadist terrorism and counterterrorism policies. Many students worldwide have participated in his massive open online course on terrorism and counterterrorism at Coursera and FutureLearn.Jeanine de Roy van Zuijdewijn is assistant professor in terrorism studies at Leiden University. Her research interests include dealing with the impact of terrorism and foreign fighters. She aims to make academic knowledge relevant for wider audiences, ranging from the general public to policymakers and politicians.