The United States Government requires every program manager in the Department of Defense to document program goals prior to the initiation of an acquisition program. According to the Defense Acquisition Guidebook (2005), an Acquisition Program Baseline (APB) satisfies this requirement. The APB describes the program goals through a list of objectives and thresholds for the cost, schedule and technical performance parameters. Updating the APB, also referred to as re-baselining, may also be required during the execution of an acquisition program. Although guidance is available for the initial production of a program baseline, scarce information on the guidance and theoretical purpose of a program re-baseline exists. The research presented in this thesis investigated the purpose and effectiveness of program re-baselines through interviews with twenty seven program managers from the acquisition community. An analysis of the data collected during the interviews, combined with an extensive review of the current literature, led to recommendations in the areas of improved guidance,practice and education. Specifically, it was revealed that the purpose of a re-baseline varies depending on an individuals past experiences with a re-baseline activity. In addition, this research revealed that a majority of program managers have participated ina program re-baseline during their careers, which magnifies the importance of clarifying the expectations and objectives of program re-baselines for those entering the acquisition profession.