This book includes an introduction to digital twin, digital twin technology, digital twin and industry 4.0, digital twin city, application of digital twin in other aspects, case studies of digital twin, challenges and development trends of digital twin technology, and the digital economic production policy. It covers many important technical points of digital twin, enumerates many cases to analyze the theory, and puts forward innovative views in various areas. In reading this book, the reader will gain a deep understanding of digital twin, an entirely new discipline.