The development from program inception of major Apollo spacecraft systems is reviewed. Those subsystems which required significant advances in current technology are highlighted, and important system development derived from Project Mercury and the Gemini Program is discussed where pertinent. The overall approach to satisfaction of mission requirements in the Apollo spacecraft is outlined in relation to the manned lunar landing.The paper illustrates that all mission-critical systems were designed with a high degree of reliability and redundancy because of the limited flight frequency, the denial of inflight maintenance, and the absence of an inflight rescue capability. For the lunar module, the first true spacecraft, significant unknowns that faced spacecraft designers could not be effectively resolved in any of the earth-orbit flight programs. Based on the unqualified success of Project Mercury and the Gemini Program, however, major state-of-the-art advances were required for the entire Apollo spacecraft in only a few subsystems such as the guidance and navigation systems and certain crew-related subsystems.A summary of the mission accomplishments to date and a discussion of future flight programs using Apollo hardware is presented. A brief projection is given as to the major development tasks which might be required in order to introduce Apollo spacecraft components into followon vehicles designed for longer duration missions.