Abstract : Experience shows that engineering commercial off-the-shelf (COTS)-based systems requires fundamental changes from traditional engineering: adjusted roles and responsibilities, new skills, and different processes. Practitioners are often surprised to find that building and supporting COTS-based systems demands more, not less, discipline in their management and engineering practices. Many organizations have derived benefit from process improvement using capability maturity models and want to apply them as they build COTS-based systems. In addition, organizations building COTS-based systems want to apply the Capability Maturity Model Integration (CMMI). This leads to the question, 'How should CMMI be interpreted for organizations building, fielding, and supporting a COTS-based system?' This report shows that developing and maintaining COTS-based systems is more than selecting products and managing vendor relationships and is, therefore, more than just applying the Supplier Sourcing discipline within CMMI. The four CMMI disciplines-Systems Engineering, Software Engineering, Integrated Product and Process Development, and Supplier Sourcing-require interpretation and must be used together to promote improvement of an organization's processes for developing and maintaining COTS-based systems. This report summarizes what makes COTS-based systems unique and provides high-level guidance for interpreting and using CMMI practices to facilitate appropriate processes for COTS-based systems.