The growing market for commercial-off-the-shelf unmanned aerial vehicles has brought with it innate rewards and vulnerabilities. Aerial technology presents unique cyber risk characteristics that must be managed in new ways. A key stage of the risk management process is risk assessment – the earlier in the lifecycle the assessment is performed, the more the security that can be designed into the operational environment.This chapter presents a quantitative risk assessment framework for unmanned aerial vehicles based on qualitative cyber measures and requirements that captures the dynamics of probability and severity. The assessment uses 14 sub-metrics that cover unmanned aerial vehicle security, temporal aspects and mission environments to express the risk as a single score ranging from 0.0 (best) to 10.0 (worst). A case study involving three popular unmanned aerial vehicle models in three mission-environment scenarios demonstrates the breadth and variability, general applicability and ease of use of the risk assessment framework. Performing risk assessments before unmanned aerial vehicle acquisition will enable organizations and individuals to accurately compare and select the best vehicles for their missions and environments.