In the years immediately following World War II, information was disclosed about what has been termed the shadow war of the existence of hitherto secret agencies. In Germany it was the Abwehr and the Sicherheitsdienst; in Britain it was MI5, the Secret Intelligence Service (MI6) and Special Operations Executive (SOE); in the United States it was the Office of Strategic Services (OSS) and the Special Intelligence Service (SIS) of the Federal Bureau of Investigation (FBI); in Japan it was the Kempet'ai; and in Italy the Servicio di Informazione Militare (SIM). Sixty years after World War II secrets are still being revealed about the covert activities that took place. Many countries had secret agencies maintaining covert operations, but even ostensibly neutral countries also conducted secret operations. Changes in American, British, and even Soviet official attitudes to declassification in the 1980s allowed thousands of secret documents to be made available for public examination, and the result was extensive revisionism of the conventional histories of the conflict, which previously had excluded references to secret intelligence sources.

The Historical Dictionary of World War II Intelligence tells the emerging history of the intelligence world during World War II. This is done through a chronology, an introduction, a bibliography, and hundreds of cross-referenced dictionary entries on the secret agencies, operations, and events. The world of double agents, spies, and moles during WWII is explained in the most comprehensive reference currently available.