What is counter-terrorism (CT)? While the answer to this question may seem self-evident, it has become quite complicated to define the contours of a field that has expanded dramatically in the two decades since the 9/11 attacks. The development of "softer" policies, dealing with the prevention of radicalisation, has blurred the limits of CT. Through the use of public policy theory and an in-depth case study on Belgium, the book identifies the key factors influencing CT policy-making, both domestically and internationally, and offers an explanation for the development of a more comprehensive CT agenda across Europe. It provides an innovative theoretical approach and is also based on extensive interviews with key counter-terrorism officials and analysis of key policy documents. The book concludes by identifying some key drivers of change and offers an embryonic theory of CT policy-making. The book will be of much interest to students and practitioners of counter-terrorism, radicalisation, European politics and security studies.