The notes and transcriptions that Alexander Vassiliev made during several years of work in the archive of the former KGB resolve many of the early Cold War’s espionage cases. Hitherto unexploited materials in the collection relate directly to the case of the diplomat Alger Hiss. They conclusively show that Hiss was, as Whittaker Chambers charged more than six decades ago, an agent of Soviet military intelligence (GRU) in the 1930s. With other evidence, Vassiliev’s notebooks also establish with very high probability that Hiss was the Soviet agent “Ales” mentioned in a much-disputed Venona cable. This article provides a systematic review of the evidence on the case.