From the Great Purges in the Soviet Union in the late 1930s to the bloody elite purges in Eastern Europe in the late 1940s and early 1950s to the mass terrorism in Cambodia in the middle 1970s, the role of terror and the secret police in Communist politics has been powerful and highly visible. This book reviews the surprisingly sparse literature on the subject and presents new studies of secret-police forces and the political use of terror in the USSR, China, Poland, Hungary, Romania, Czechoslovakia, and Cambodia. The focus of each country study is the nature and extent of internal terror and repression, the range of external intelligence functions, and the effect of secret-police interference in internal policymaking processes. The book ably fills a void in the literature by providing needed case studies as well as a theoretical framework for understanding secret-police activity.