Countering recent hype around technology, a leading expert argues that the endurance of dictatorship in China owes less to facial recognition AI and GPS tracking than to the human resources of the Leninist surveillance state. For decades China watchers argued that economic liberalization and increasing prosperity would bring democracy to the world's most populous country. Instead, the Communist Party's grip on power has only strengthened. Why? The answer, Minxin Pei argues, lies in the effectiveness of the Chinese surveillance state. And the source of that effectiveness is not just advanced technology like facial recognition AI and mobile phone tracking. These are important, but what matters more is China's vast, labor-intensive infrastructure of domestic spying. Central government data on Chinese surveillance is confidential, so Pei turned to local reports, police gazettes, leaked documents, and interviews with exiled dissidents to provide a detailed look at the evolution, organization, and tactics of the surveillance state. Following the 1989 Tiananmen uprising, the Chinese Communist Party invested immense resources in a coercive apparatus operated by a relatively small number of secret police officers capable of mobilizing millions of citizen informants to spy on those suspected of disloyalty. The CCP's Leninist bureaucratic structure-whereby officials and party activists penetrate every sector of society and the economy, from universities and village committees to delivery companies, telecommunication firms, and Tibetan monasteries-ensures that Beijing's eyes and ears are truly everywhere. While today's system is far more robust than that of years past, it is modeled after mass surveillance implemented under Mao Zedong and Chinese emperors centuries ago. Rigorously empirical and rich in historical insight, The Sentinel State is a singular contribution to our knowledge about coercion in the Chinese state and, more generally, the survival strategies of authoritarian regimes.