In 1995, the NASA Systems Engineering Handbook (NASA/SP-6105) was initially published to bring the fundamental concepts and techniques of systems engineering to the National Aeronautics and Space Administration (NASA) personnel in a way that recognized the nature of NASA systems and the NASA environment. Since its initial writing and its revision in 2007 (Rev 1), systems engineering as a discipline at NASA has undergone rapid and continued evolution. This revision (Rev 2) of the Handbook maintains that original philosophy while updating the Agency's systems engineering body of knowledge, providing guidance for insight into current best Agency practices, and maintaining the alignment of the Handbook with the Agency's systems engineering policy.The update of this Handbook continues the methodology of the previous revision: a top-down compatibility with higher-level Agency policy and a bottom-up infusion of guidance from the NASA practitioners in the field. This approach provides the opportunity to obtain best practices from across NASA and bridge the information to the established NASA systems engineering processes and to communicate principles of good practice as well as alternative approaches rather than specify a particular way to accomplish a task. The result embodied in this Handbook is a top-level implementation approach on the practice of systems engineering unique to NASA.