Digital Human Modeling and Medicine: The Digital Twin explores the body of knowledge and state-of-the-art in Digital Human Modeling (DHM) and its applications in medicine. DHM is the science of representing humans with their physical properties, characteristics and behaviors in computerized, virtual models. These models can be used standalone or integrated with other computerized object design systems to both design or study designs of medical devices or medical device products and their relationship with humans. They serve as fast and cost-efficient computer-based tools for the assessment of human functional systems and human-system interaction. This book provides an industry first introductory and practitioner focused overview of human simulation tools, with detailed chapters describing body functional elements and organs, organ interactions and fields of application. Thus, DHM tools and a specific scientific/practical problem – functional study of the human body – are linked in a coherent framework. Eventually the book shows how DHM interfaces with common physical devices in medical practice, answering to a gap in literature and a common practitioner question. Case studies provide the applied knowledge for practitioners to make informed decisions.