Publisher Summary This chapter describes the engineering behind fault detection and mitigation. The chapter explains the fault detection and failsafe mechanisms that are put in E-2. The chapter presents two of the most interesting reports: (1) the report on the demise of the European Space Agency's first Ariane-5 rocket and (2) the report on the failures of the Therac-25 radiotherapy units. Failures in E-2's software and firmware or loss of the craft represent a huge financial setback. As a result, the firmware is structured towards recovery of the vehicle after any failure, reflecting the design priorities. If this were a government project, it would quite possibly be designed with data security as its first priority—the hardware would be considered expendable.