When it first appeared in 1967, Kahn's book on cryptography received warm reviews from both experts and an appreciative lay audience. With panache and scholarly authority, it covered such famous cryptographic stories as the Austrian empire's superbly efficient "black chamber" in the eighteenth century, the Dreyfus Affair, and the antics of Herbert Yardley, the bizarre genius whose successful attack on secret Japanese communications enabled the United States to outmaneuver Japan at the Washington Naval Conference of 1921-22. In 1967, however, the big story had yet to come out publicly, namely that the British, later assisted by the United States, had mounted the most successful codebreaking effort in history against Nazi Germany during World War II. Unfortunately, this barely revised version of a classic work assigns this and other major stories that have come out in the last three decades to an inadequate additional chapter just 14 pages long. A pity, because Kahn has continued to publish important works on this subject in the intervening decades. Understanding, then, that this is more a reprint than a revision, readers may still consult it with profit and interest.