In any society some people pose a risk to others. For hundreds of years preventive detention has been authorised by governments to ensure people are available for criminal proceedings (e.g. remand), in the mental health area, for quarantine, for inebriates, enemy aliens, and sexual predators. The policy has also been famously employed more recently to control suspected terrorists. These regimes have proliferated in recent years, and this book asks and answers some of the fundamental questions about these regimes. What are their doctrinal foundations? Is there a risk in laws that blur the historic division between criminal and civil law, allowing civil law to be used for criminal law purposes but without the protection normally provided to criminal defendants? Are they effective in protecting people from harm? How do these regimes challenge fundamental principles, such as human rights? Are our laws and policies geared towards the rehabilitation of the detained? What are the remedies available to people who seek to challenge these regimes? Regimes that punish people who have not been convicted of a fresh crime or that contemplate the infliction of punishment upon breach of a 'control order' require careful scrutiny to avoid human rights abuse. This volume considers preventive detention in its many varying forms across Europe, the Americas and Australasia, interrogates the theoretical underpinnings of the regimes, and then critically analyses these regimes for consistency with international human rights. The volume brings together respected international experts to guide lawmakers, policymakers and academics in an increasingly significant area of penal and public policy.