Security is the main objective of civil aviation. How safe is safe, that is to say, when something can be considered safe, is a question that concerns all human activities. The integration of human-powered aircraft in the civil aviation system is based on the principle that the existing level of safety must not be compromised by the use of these aircraft. The book briefly discusses the risks inherent in the operation of remotely piloted aircraft, discusses the concept of risk, analyzes the security implications of operations, and, in particular, addresses the category of remotely piloted aircraft weighing less than 25kg , provides some guidance on how to conduct an assessment of the risks that could be caused by their use, in order to verify their suitability for operations.