When the landmark Non-Proliferation Treaty was signed in 1968, the phrase 'cessation of the nuclear arms race at an early date' (Art. VI) was commonly understood to mean a comprehensive test ban (and a ban on the production of fissionable materials). That year, Norway and the United States agreed to build a large seismic array facility in south-eastern Norway (NORSAR), financed by the US, with a view to verification of a comprehensive ban. These were times of maximum secrecy and minimal trust: for the Americans, Soviet tests were of particular interest, and US tests not registered by NORSAR would presumably not be detected by the Soviets either. However, when the Cold War ended and seismic registrations were checked against US and Soviet test records, NORSAR had them all. In the Group of Scientific Experts that prepared the International Monitoring System for the Comprehensive Test Ban Treaty (CTBT), eminent members of the NORSAR staff played important roles from the beginning. The book chronicles NORSAR’s contributions to the adoption of the CTBT in 1996, and later in support of the Preparatory Commission of the CTBT Organization in Vienna. Throughout, the authors are careful to situate NORSAR’s technical work in the international political context. The Treaty is waiting for more ratifications in order to enter into force. In the meantime, the P5 moratoria on nuclear testing still holds. The sustained effort to prohibit all nuclear testing is the most notable Norwegian contribution to arms control so far. The Executive Summary is a good guide to the main text, which is well written and accessible not only to arms controllers but also to interested people without technical qualifications.