The climate crisis, inequality, poverty, disease, hunger, food waste, and loss of biodiversity are all part of an extensive list of global challenges impacting us at a local level that could be addressed better by using the One Health approach. In a world where people, animals and the environment are recognized as being interconnected and interdependent, we need to work together to improve the health of people, plants, animals and ecosystems simultaneously. One Health provides the thinking, concepts, tools, and practical approaches needed to tackle health problems in a collective and collaborative way. But what is One Health, and how can we implement it in our everyday life? This textbook provides an easy to understand, straightforward description of One Health concepts, principles and methods, structured around core competencies so that everyone can contribute to addressing today's most profound global problems more efficiently and effectively. As an entry-level learning resource for anybody with an interest in better understanding and implementing One Health, it is a comprehensive yet accessible introduction for undergraduate and postgraduate students, practitioners, decision-makers and researchers across a wide range of subject specialisms.