This study on detention fills a gap in scholarship on China's criminal justice system. This article describes shuanggui, a form of detention used on Party members. It traces the historical legacies linking shuanggui to forms of detention practiced in imperial China and in Chinese Communist Soviets. The article then moves on to describe the birth of shuanggui and the evolution of norms regulating it. Finally, it points out how shuanggui is being regularized and institutionalized. This process is leading towards its gradual abolition or amelioration. On the other hand, it reflects the continuing evolution and sophistication of the power of the Chinese party-state.