For FY 2014, the Department of Defense (DOD) requested over $11 billion to modify existing weapon systems -- more than 10% of its total procurement budget. Traditionally, DOD has acquired proprietary systems, which are costly to upgrade and limit opportunities for competition. Through its Better Buying Power initiatives, DOD has re-emphasized the use of an open systems approach as a way to reduce costs through effective competition. This report examined DOD's progress in implementing an open systems approach for Unmanned Aircraft Systems (UAS) acquisitions. It addresses (1) the characteristics and benefits of an open systems approach; (2) DOD's efforts in implementing an open systems approach for its UAS portfolio; and (3) challenges, if any, DOD is encountering in implementing this approach. Figures. This is a print on demand report.