Drug development is the industrial process through which it becomes possible that a lead candidate is advanced from drug discovery to a marketed product including all preclinical and clinical developmental steps. The preclinical development steps are: (1) characterization, (2) scale-up of the production process, (3) GMP transfer of the production process, (4) GMP transfer of the quality control, (5) formulation of active pharmaceutical ingredient, (6) stability testing, (7) toxicity profile of the drug in animal model, and (8) dose and application schedule of the drug in animal model. The clinical development steps are in particular Phase I toxicity, Phase II efficacy, and Phase III registration trial. The specific challenge in the case of boron neutron capture therapy (BNCT) is the bimodality of the therapy, i.e., the combination of the drug and the neutron source, which is discussed in this chapter.