This chapter introduces the essentials of the management of the radioactive legacy of nuclear energy use, with a focus on the safe disposal of high-level radioactive waste from commercial electricity generation. While there is an international consensus that the responsible disposal of this waste can only be achieved through isolation in deep geological repositories, the analysis shows that the implementation of this solution has been delayed globally, despite the fact that international conventions and organizations have long aimed to support this goal. Using Germany as an example, this chapter illustrates why disposal has so far failed, even in a highly industrialized country with favorable geological conditions and early regulatory initiatives. In summary, the precautionary principle regarding the risks of the “back-end” of nuclear energy use has been and will likely continue to be violated for a long time to come.