The acquisition process for a new weapon system involves developing a set of technical requirements-a set of statements or models defining what a system should do and how well it should do it-for the system's design to ensure that the system provides the needed operational capability within budget and schedule constraints. However, oversights during this process can result in cost or schedule overruns, unsuitable operational performance, or outright cancellation. The U.S. Department of the Air Force (DAF) asked RAND Project AIR FORCE to develop an approach to help improve DAF's technical requirements development process. To do so, the authors consulted policies and the literature, held discussions with DAF stakeholders and subject-matter experts, conducted two case studies, and assessed various tools that might assist development of technical requirements. This report describes the resulting approach, which has been informed by systems-based methods and tools, and includes an exploration of the applicability and feasibility of one specific emerging hazard-analysis tool: system-theoretic process analysis (STPA).