This book brings together leading counterterrorism experts, from academia and practice, to form an interdisciplinary assessment of the terrorist threat facing the United Kingdom and the European Union, focusing on how terrorists and terrorist organisations communicate in the digital age. Perspectives drawn from criminological, legalistic, and political sciences, allow the book to highlight the problems faced by the state and law enforcement agencies in monitoring, accessing, and gathering intelligence from the terrorist use of electronic communications, and how such powers are used proportionately and balanced with human rights law. The book will be a valuable resource for scholars and students of terrorism and security, policing and human rights. With contributions from the fields of both academia and practice, it will also be of interest to professionals and practitioners working in the areas of criminal law, human rights and terrorism.