The harmonious coexistence of humans and machines evolves beyond a simple user-machine dynamic into a more interactive, complementary, and supportive ecosystem. This work investigates the human motion digital twin to drive human–robot collaboration in smart manufacturing. The application of human motion digital twin offers substantial support for improving human–robot interaction in this context. On the basis of this trend, this work introduces the research background and significance of digital twin technology in relation to human motion. It then systematically reviews the related work of key technologies for developing human motion digital twin. At last, the main research content and chapter organization of this book are outlined. It emphasizes the in-depth exploration of human motion digital twin within the context of smart manufacturing. This research establishes a roadmap for scalable, human-centric automation-balancing operational efficiency with workforce adaptability in next-gen manufacturing system.