Terrorism - political violence against civilians meant to inspire fear in a wider audience, usually carried out by non-state actors - has occurred for millennia and has been studied seriously by researchers since at least the 1970s, while the attacks of Sept. 11, 2001, and subsequent wars have brought a considerable amount of attention to the topic in the ensuing decades. What Do We Know about Terrorism? addresses these developments, engaging with key topics such as definitions of terrorism, terrorism and social media, terrorism in civil war, and deradicalization. Timely chapters written by scholars review what we know about various topics related to terrorism and describe the empirical research findings in the academic literature. The book also includes many historical and modern examples of terrorist groups and attacks to ground the theoretical ideas into concrete illustrations for students. This accessible and cutting edge overview helps students learn about terrorism and political violence, fitting in with many of the topics that come up in relevant classes.