The technological marvel that made the Apollo missions to the Moon possible was the onboard computer. In the 1960s, most computers filled an entire room, but the spacecraft's computer had to be compact and energy-efficient. Although it is hard for people today to accept that it was possible to control a spacecraft with such a primitive computer, it still had capabilities that are advanced even by today's standards. This is the first book to fully describe the architecture, command format, and programs used by the astronauts of the Apollo guidance computer. As a comprehensive report, it will cover the disciplines of computer science, electrical engineering, and aerospace engineering. However, it will also be accessible to space enthusiasts. In short, the intention is for this to be the definitive report on the Apollo guidance computer. Frank O'Brien's interest in the Apollo program is evident.