Improving the U.S. Department of Defense (DoD) acquisition system-the management and development processes by which the department acquires, develops, and sustains weapon systems, automated information systems, and services-has been an issue of sustained interest to policymakers since the beginning of the military establishment. Numerous actions have been initiated and implemented over decades to rein in the increasing life-cycle costs and to ensure a timely delivery of these systems to meet U.S. security needs. In this report, researchers describe overarching trends that affect the defense acquisition system, outline challenges in DoD's defense acquisition process, and suggest improvements that might help address those challenges. The study is informed by open-source documents and insights from publicly available RAND Corporation research on defense acquisition, especially reports published since 1986, when a similar review of RAND research was published.