The metaverse is sweeping the global thanks to its fundamentally innovative concepts of physical-virtual blended reality and years of industrial efforts on relevant hardware development. It is yet unclear what the metaverse is, what technologies it relies on, and what concern the society should care about since it is such a huge ecosystem with nearly  unlimited possibilities. The book aims to provide a comprehensive study o n the metaverse including its development and ecosystem, and detailed descriptions of multiple key technologies with their challenges and state-of-the-art solutions, finally conclude with several important societal issues the metaverse may raise including concerns and suggestions. The book targets at providing understandable introductions to varied aspects of the metaverse that may appearnew to common audiences, and, deep insights into a number of key directions for related professionals. The purpose of the book is to help readers better understand the concept and current status of metaverse while inspiring relevant readers or institutes to spot interesting and challenging topics to follow.