Unmanned aircraft or Drones, as they are widely known, have been used for military purposes as well as within the framework of scientific and research initiatives since the 1960s. However, in the last decade they have experienced significant development, mainly due to rapid technological advancements, increasing interest in their use in various everyday applications. The "Book of Drones" contains all the necessary knowledge about the technologies used in Drones, specialized information about the systems they are equipped with, as well as details about their applications in different areas of modern society. The first section of the book provides a brief historical overview of their evolution, presents the specialized terms used, and describes their categories, followed by a description of the basic elements of aerodynamics, communications, and automatic control systems used. It also presents the principles of operation and information about flight instruments, the basic elements of aerial photography, as well as control and navigation characteristics. The second section provides a comprehensive overview of information that significantly affects the utilization of unmanned aircraft, such as the institutional framework in Greece and Europe, air traffic control, and basic meteorological elements that affect drone flights. It also presents the impact of human factors, flight safety, and challenges related to privacy and ethics arising from their use. The last section presents all the modern applications of unmanned aircraft, in military operations and missions, in security and policy protection, in teleobservation and photogrammetry, in precision agriculture, as well as in journalism and mass media, while also describing the possibilities for protection against their malicious use.