In recent decades, there have been numerous attempts to rein in the cost growth of U.S. Department of Defense (DoD) acquisition programs. Cost growth is the ratio of the cost estimate reported in a program's final Selected Acquisition Report (SAR) and the cost-estimate baseline reported in a prior SAR issued at a particular milestone. Drawing on prior RAND research, new analyses of completed and ongoing weapon system programs, and data drawn from SARs, this study addresses the following questions: What is the cost growth of DoD weapon systems? What has been the trend of cost growth over the past three decades? To address the magnitude of cost growth, it examines cost growth in completed programs; to evaluate the cost growth trend over time, it provides additional analysis of a selection of ongoing programs. This sample of ongoing programs permits a look at growth trends in the more recent past. Changes in the mix of system types over time and dollar-weighted analysis were also considered because earlier studies have suggested that cost growth varies by program type and the cost of the program. The findings suggest that development cost growth over the past three decades has remained high and without any significant improvement.