What limits, if any, should be placed on a government’s efforts to spy on its own citizens in the name of national security? Recent battles over privacy have been dominated by fights over warrantless electronic surveillance and CCTV; the coming years will see debates over DNA databases, data mining, and biometric identification. There will be protests and lawsuits, editorials and elections resisting these attacks on privacy. Those battles are worthy. But the war will be lost. Modern threats increasingly require that governments collect such information, governments are increasingly able to collect it, and citizens increasingly accept that they will collect it. This book proposes a move away from questions of whether governments should collect information and onto more problematic and relevant questions concerning its use. By reframing the relationship between privacy and security in the language of a social contract the book offers a framework to defend freedom without sacrificing liberty.