This book introduces the concept of digital twins and their purposive usage, including the technology infrastructure and the method support necessary for their construction. The landscape of digital twins is illustrated through a range of use cases spread across different application domains such as strategy and business assessment in enterprises, logistics networks, manufacturing industries, chemical and refinery systems, sustainable food ecosystems, and public healthcare.  All these examples show how digital twins are exploited to simulate complex scenarios depending on various external factors – all of which would not be feasible as real-world simulations because of their high costs, potential fatal damages, and unpredictable side effects. The book is written for professionals in industry who would like to learn about the application of these powerful methodologies and tools in various areas as well as for researchers in computer science who would like to draw inspirations for further development of this technology from real-world applications.