Google Zanzibar is a globally distributed authorization system capable of processing over 10 million client queries per second. It was built by Google to address the limitations of their previous permissions systems and to provide a flexible, scalable, and reliable solution for managing user and data relationships across multiple applications and services. The system uses a directed graph representation of relationships between users, resources, and other entities to compute permissions decisions, which are then made available through an API that can be used by developers to outsource their user and data relationships. Zanzibar achieves low latency and high scale by distributing its load across thousands of servers organized in clusters around the world, using caching and consistent hashing to improve performance, and leveraging Google's planet-scale database system, Spanner, for data storage. The system also includes features such as request hedging and denormalization to further reduce tail latencies.