Surveillance presents a conundrum: how to ensure safety, stability, and efficiency while respecting privacy and individual liberty. From police officers to corporations to intelligence agencies, surveillance law is tasked with striking this difficult and delicate balance. That challenge is compounded by ever-changing technologies and evolving social norms. Following the revelations of Edward Snowden and a host of private-sector controversies, there is intense interest among policymakers, business leaders, attorneys, academics, students, and the public regarding legal, technological, and policy issues relating to surveillance. This handbook documents and organizes these conversations, bringing together some of the most thoughtful and impactful contributors to contemporary surveillance debates, policies, and practices. Its pages explore surveillance techniques and technologies; their value for law enforcement, national security, and private enterprise; their impacts on citizens and communities; and the many ways societies do-and should-regulate surveillance.