This book introduces the theory and practice of ecological risk management. Using recent and live case studies in Japan, the book explains the use of basic mathematical techniques in extinction risk, adaptive population management, avian collision risk in wind farms, potential biological removal for marine mammals, and ecological risk assessment of heavy metals. The focus of this book is on case studies of nature conservation in Japan, including internationally renowned topics of Japanese fisheries, Shiretoko World Heritage, Fukushima Daiichi Nuclear Power Plant accident. It also covers the adaptive risk management of the new coronavirus disease. The book comprises four parts covering ecotoxicology, fisheries, wildlife management and conservation, and ecosystem-based management. It differs from other books in having its primary interest in human impacts on animals, plant, and ecosystems, while existing works in this area concentrate on the fate of toxic substances in the environments and their effects on humans. This book is unique in that it indicates various environmental issues that the theoretical ecology is potentially applicable without concentrating into any particular subject such as ecotoxicology or conservation biology.  Primary readers are undergraduate/graduate students, staffs of environmental consultant companies and environmental NPOs, and journalists. Readers will find this book useful for its abundant information on case studies of ecological risk management and consensus building in Japan.