This book examines the risks to freedom of expression, particularly in relation to the internet, as a result of regulation introduced in response to terrorist threats. The work explores the challenges of maintaining security in the fight against traditional terrorism while protecting fundamental freedoms, particularly online freedom of expression. The topics discussed include the clash between freedom of speech and national security; the multijurisdictional nature of the internet and the implications for national sovereignty and transnational legal structures; how to determine legitimate and illegitimate association online; and the implications for privacy and data protection. The book presents a theoretical analysis combined with empirical research to demonstrate the difficulty of combatting internet use by terror organizations or individuals and the range of remedies that might be drawn from national and international law. The work will be essential reading for students, researchers and policy makers in the areas of Constitutional law; Criminal Law, European and International law, Information and Technology law and Security Studies.