This book introduces the transition technologies for migrating from IPv4 to IPv6, a process initiated by the Internet Engineering Task Force (IETF) with the release of the IPng (IPv6) protocol standard in 1998. Despite the passage of 25 years, the adoption of IPv6 has been slow. To address this challenge, this book presents innovative solutions based on stateless translation technology tailored for various IPv6-only scenarios. Exploring Internet architecture and design principles, it demonstrates why the stateless translation-based scheme is not only feasible but essential for achieving IPv6 single-stack Internet. The solutions presented in this book are rooted in the authors' extensive experience designing, managing, and operating the China Education and Research Network (CERNET) and its transition to IPv6. These methods have been thoroughly tested and validated through prototypes and commercial products deployed on large-scale operational networks. The authors' active roles as co-authors of IETF standards further ensure that the content combines both theoretical expertise and practical implementation. Enriched with numerous case studies, this book illustrates IPv6-only, IPv6-mostly, and IPv4 as a Service solutions across a range of network scenarios, including campus and enterprise networks, backbone networks, metropolitan area networks, data centers, exchange points, and virtual private networks. Whether you are a researcher, developer, or network operator, this book offers valuable insights and practical designs to help you quickly and effectively engage with IPv6 transition technologies. The translation of this book was done with the help of artificial intelligence. A subsequent human revision was done primarily in terms of content.