A book published by the author in 1993 contained a lengthy chapter on the August 1991 coup attempt in the Soviet Union. This article builds on and updates that chapter, making use of a trove of newly available documents and memoirs. The article discusses many aspects of the coup attempt, but it particularly seeks to explain why the coup failed and what the implications were for the Soviet Union. The events of December 1991 that culminated in the dissolution of the Soviet Union were the direct result of changes set in motion by the failed coup. The major state and party institutions that might ordinarily have tried to hold the country together—the Communist Party apparatus, the secret police, the military-industrial complex, the Ministry of Defense, and the state administrative organs—all were compromised by their participation in the coup. As a result, when events pushed the Soviet Union toward collapse there was no way of staving off that outcome.