This chapter outlines the methylmercury poisoning in Minamata (MPM): about the history, symptom pathogenesis, research on the causal agent, and responses of the national and local governments and the responsible company, i.e., Chisso, to the outbreak of MPM. A book written by Nishimura and Okamoto (2001) played an important role to clarify the mechanism of the MPM outbreak. Based on this book and the published data on mercury concentrations of aquatic organisms and newborns' umbilical cords, how methylmercury generated in the plant, flew into the sea, transferred to aquatic organisms, and was consumed by residents are explained. Victims of MPM, compensation and environmental restructure, and court ruling against this incident are described. Based on lecture notes from a university course, students' suggestions for avoiding a repeat of the tragedy are also introduced.