The book "Letter on the Organization of Posts and Relays" by S. Dugas is a documentary-historical work that examines the system of postal services and relay points. The author examines in detail the important aspects of the organization of these services in French society, which ensured the efficient and rapid transmission of letters and messages. The book contains information about the history of the development of the postal system, its structure, operating principles and impact on society. This is a valuable resource for those interested in the history of communications and the organization of public services.