The Cold War was a global conflict between intelligence agencies as well as governments. From the construction of the Soviet bloc in the aftermath of the Second World War to the war in Afghanistan and US operations against the Sandinistas in the 1980s, the course of that global conflict cannot be adequately interpreted without an understanding of its intelligence dimension. Attempting to resolve the most difficult problem posed by the Cold War - why it did not end in hot war - also requires an understanding of the stabilising role of secret 'national technical means’ based on a combination of IMINT and SIGINT. There were major differences, however, between intelligence assessment, as well as the priority given to scientific and technological intelligence, in East and West. Intelligence communities also had a far more central role in the one-party states of the Soviet bloc than in Western democracies, even at their most irresponsible. At the end of the Cold War, the speed of the collapse of the Soviet system took almost all observers (including Western intelligence agencies) by surprise. What now seems most remarkable, however, is less the sudden disintegration of the Soviet Union at the end of 1991 than its survival for almost seventy-five years. Without the KGB’s immense system of surveillance and social control, the Soviet era would have been significantly shorter. The KGB’s most enduring achievement was thus to sustain the longest-lasting one-party state of the twentieth century. By postponing the collapse of the Soviet Union, the KGB also prolonged the Cold War.