Book excerpt: The attention of many developed countries has increasingly focused on the security and protection of critical infrastructure. The use of Unmanned Systems (USs) for this purpose has been growing rapidly in recent years, as advances in technology, increased versatility and smaller size, together with the reduced risks and costs associated with removing the need for a pilot or operator on board, have all made these systems more attractive. This book, Monitoring and Protection of Critical Infrastructure by Unmanned Systems, presents 15 papers delivered at the NATO Advanced Training Course (ATC) of the same name hosted in Chisinau, the Republic of Moldova, from 30 May to 5 June 2022. This event was held in a hybrid format, and was attended in-person by 12 of the 31 speakers and the majority of the 92 attendees. The aim of the ATC was to explore the monitoring and protection of critical infrastructure using USs. Various USs, including ground control stations (GCS), data communication links, and a range of unmanned aerial (UAV), ground (UGV) and underwater (UUV) vehicles are covered, and the papers included here also deal with topics such as the use of drones for buildings inspection and the new technologies which can help with the recognition and monitoring of anthropogenic threats and natural hazards. There is also a focus on data analysis and modeling. Providing an overview of the use of unmanned vehicle systems and sensor-network technology for monitoring and protection, the book will be of interest to all those working to protect critical infrastructure.