This well-edited collection of articles is an excellent addition to the growing literature on Bletchley Park's codebreaking achievements. There is a good deal of previously unpublished information and some interesting personal memoirs. There are summary articles that help place the wartime codebreaking triumphs in a much broader and more balanced perspective than earlier publications, and others that give some overdue recognition to contributions from organizations other than the better-known Enigma- and Tunny-breaking operations. The book also helps locate Bletchley's wartime achievements within a wider pre- and post-war context. Readers unfamiliar with the Bletchley Park story might want to read "Codebreakers" by Hinsley and Stripp as a prelude to "Action This Day".