This illuminating book offers a timely assessment of the development and proliferation of precursor crimes of terrorism, exploring the functions and implications of these expanding offences in different jurisdictions. In response to new modes and sources of terrorism, attempts to pre-empt potential attacks through precursor offences have emerged. This book examines not only the meanings and effectiveness of this approach, but also the challenges posed to human rights and social and economic development. Featuring contributions from leading academic and practitioner experts in counter-terrorism law, the book covers the broad scope of activities tackled by these new legal interventions, including membership, collaboration, communications, training and financing. Taking a comparative approach that relies on extensive experience in various jurisdictions, including the UK and Spain, the chapters also discuss important related issues such as international cooperation, investigations and penology, offering insights into the context of policies and practices. Scholars and advanced students of criminal and human rights law with an interest in terrorism and terrorism offences will find this book essential reading. It will also benefit legal practitioners and policy makers in fields such as international criminal law cooperation and counter-terrorism.