The fourteen chapters in this book explore different aspects of the history of spying and secret diplomacy, with an ambitious chronological and geographical range that covers everything from late medieval Italy to the first British Empire. After a short historiographical introduction (7–20) that helpfully cites a wealth of scholarship in French and German as well as English, the first two chapters of this book offer general interpretations of early modern espionage. Lucien Bély (21–35) proposes the concept of informativité in order to turn histories of espionage away from the escapades of individual spies and towards a study of deeper social structures, before Sebastian Becker (37–57) presents a clear and well-supported plea for historians to acknowledge the importance of economic espionage in the early modern period. The following chapters by Loss (59–69) and Genêt (71–83) ask whether spying was a profession in the early modern period, in the first case by following references to the “Master of Spies” (Dominus spiarum) in Bologna between 1294 and 1604, and in the second by reconstructing the careers of two long-serving secret agents of the eighteenth century, Simon Louvrier and Johannes Kaspar von Thürriegel. In addition to the ample literature cited by Loss and Genêt, a reader interested in spying as a profession can also be pointed to Ioanna Iordanou's 2018 book, Venice's Secret Service.

The next two chapters focus on communication. Camille Descenclos (85–103) offers a helpful overview of cryptography in sixteenth-century France, showing that practitioners of this art sought to balance secrecy with speed of transmission. Next, Matthias Pohlig's chapter (105–23) demonstrates that the postal service was a key arena of early modern spying, with letters providing spies with easy access to information that would have been difficult or impossible to obtain by other means. The remaining chapters of this book dwell on more specific case studies. Alain Hugon (125–42) analyzes the 1676 autobiography of a Spanish spymaster active in the Kingdom of Naples, Antonio Pérez de Navarrete, while Serge Brunet presents a history of French agents in the service of the king of Spain during the Wars of Religion (143–70). A study (171–96) of the network assembled by one spymaster of the time, Francés de Álava. Fabrice Micallef's chapter (197–210) on the Savoyard spy René de Lucigne convincingly argues that the rules of courtly sociability governed intelligence gathering by early modern spies.

These chapters focus on Western Europe, above all on France and Spain. However, the final three chapters of this book also consider spying further east. This drift begins with Léopold Auer's chapter (211–24) on Prince Eugene of Savoy, whose responsibilities included gathering information on the Ottoman Empire. Indravanti Félicité (225–40) explores Johann Albrecht von Mandelsloh's travels through Persia and northern India in the mid-seventeenth century, using his notebooks to question whether other European visitors to the east who have been thought of only as travelers may instead have doubled as secret agents. Finally, Nikolas Pissis (241–53) brings to light dozens of Greeks in the Ottoman Empire who spied for Muscovy at around the same time, a topic that he has explored at greater length in his book Russland in den politischen Vorstellungen der griechischen Kulturwelt (2020).

Some themes recur across the vast swaths of time and space covered in this book. Almost every chapter considers motivations for spying, with money and religious confession being the two most commonly encountered. Espionage in the postal system is raised throughout this book and would doubtless reward further examination. More than one chapter also suggests that histories of espionage should stop recounting anecdotes and evaluate structures instead. Yet I am not convinced that it would benefit early modern history as a discipline to neuter a topic well placed to interest a wider public, particularly as accurate analysis and the effective use of anecdote are not mutually exclusive.

Despite its title and external appearance, this book is predominately written in French rather than in English. The chapters by Bély, Desenclos, Hugon, Brunet, Micallef, Auer, and Félicite are French, and the remainder are in English.