"Remarkable. . . Ferris's account avoids sensationalism. It provides a careful judgment of Bletchley Park's impact, points to how signals intelligence during the Cold War usefully illuminated the lower levels of the Soviet system, and shows GCHQ's operational importance to the conduct of colonial and postcolonial conflicts, including the 1982 Falklands War." - Foreign Affairs

"Fascinating . . . [Ferris] has rescued several great women codebreakers from obscurity . . . This monumental work completes the authorised picture of a century of British intelligence, a testament to how far Britain has moved away from the cult of official secrecy." - The Times

"A fascinating tale [that] takes us with the codebreakers - mathematicians, linguists, teachers and philosophers and eccentrics - through the ages of radio, telegrams telephone and satellites to the digital present." - Financial Times

"GCHQ emerges from the shadows . . . The story of the codebreakers is in fact a parallel history of the entire twentieth century . . . There is intriguing detailing of the organisation's structure and systems . . . Illuminating . . . Absorbing." - Spectator

"A book of revelation . . . Although he spent months sifting the papers in a high-security Cheltenham vault, [Ferris] does not lose sight of the big picture . . . Today, [Ferris] argues, greater openness about intelligence gathering does not affect its relevance and power. His book is an example of this, and shows that the abandonment of Cold War levels of secrecy about GCHQ benefits us all." - Sunday Times

"A global tale of mathematics, engineering, data sciences and linguistics in the service of politics, diplomacy, war and security." - Nature

"In Ferris we have a shrewd and scrupulous historian . . . GCHQ shows it is alert to the role of a security and defence agency in a modern democracy, and Ferris is to be congratulated for shedding so much light upon it." - Scotsman

"The book is at its best when sifting the role of signal intelligence (Sigint) in the Falklands war and other late imperial conflicts such as Indonesia and Palestine . . . Comprehensive." - The Guardian

"A deeply learned, comprehensive account of [GCHQ's] achievements and occasional failures." - Daily Telegraph

"Ferris offers sharp judgments of the successes and failures of British communications intelligence and its personnel." - The Michigan War Studies Review