In 2007-08, we began an investigation of problems, issues, and opportunities that arise during the acquisition of software systems that rely on open architectures and open source software. The current effort funded for 2009-10 (funding received in 2010) seeks to continue and build on the results in this area while refining its focus to center on the essential constraints and tradeoffs we have identified for software-intensive systems with open architecture (OA) and continuously evolving open source software (OSS) elements. The U.S. Air Force, Army, and Navy have all committed to an open technology development strategy that encourages the acquisition of software systems whose requirements include the development or composition of an OA for such systems, and the use of OSS systems, components, or development processes when appropriate. Our goal is to further develop and document foundations for emerging policy and guidance for acquiring software systems that require OA and that incorporate OSS elements. This report documents and describes the findings and results that we have produced as a result of our research into the area of the acquisition of software systems that rely on OA and OSS.