Scholars have long argued that international organizations help promote cooperation among states by encouraging transparency in global governance. In this groundbreaking book, Carnegie and Carson show that the story is actually more complicated. In fact, surprisingly, international organizations often work hard to keep secrets. Organizations such as the United Nations, the World Trade Organization, and the International Atomic Energy Agency have stored sensitive information confidentially to better implement peacekeeping missions, combat drug trafficking, enforce sanctions regimes, and address environmental degradation. The authors develop a theory to explain when cooperation is better served through the safeguarding of private information and when it is better served by its disclosure. Having general information about whether particular states uphold commitments is critical for the enforcement of rules and agreements. But the disclosure of some sensitive information can be counterproductive. For instance, publishing satellite photos of a country’s hidden nuclear weapons can lead to greater efforts at concealment. Publishing information regarding the health of a country’s financial sector could lead to an adverse market reaction, compounding the problem. The book explores these complexities in detailed empirical studies in the areas of nuclear proliferation, international trade, and war crimes. The challenge for international organizations is formidable: their legitimacy as intergovernmental bodies hinges on their openness and accountability, but their effectiveness as problem solvers depends in part on their ability to guard secrets.