Intelligence activities have always been an integral part of statecraft. Ancient governments, like modern ones, realized that to keep their borders safe, control their populations, and keep abreast of political developments abroad, they needed a means to collect the intelligence which enabled them to make informed decisions. Today we are well aware of the damage spies can do. Here, for the first time, is a comprehensive guide to the literature of ancient intelligence. The entries present books and periodical articles in English, French, German, Italian, Spanish, Polish, and Dutch—with annotations in English. These works address such subjects as intelligence collection and analysis (political and military), counterintelligence, espionage, cryptology (Greek and Latin), tradecraft, covert action, and similar topics (it does not include general battle studies and general discussions of foreign policy). Sections are devoted to general espionage, intelligence related to road building, communication, and tradecraft, intelligence in Greece, during the reign of Alexander the Great and in the Hellenistic Age, in the Roman republic, the Roman empire, the Byzantine empire, the Muslim world, and in Russia, China, India, and Africa. The books can be located in libraries in the United States; in cases where volumes are in one library only, the author indicates where they may be found.