This Chapter explores the concept of Metaverse in depth, focussing on its development from the virtual worlds to modern digital environments. In particular, it describes the architecture of Metaverse, emphasising the layers that allow for present-day virtual experiences and the main concepts that inform them. Moreover, the chapter examines several technological advancements, namely, blockchain, VR/AR, and AI, that play significant roles in the functioning and improvement of Metaverse and the interaction of its users. Furthermore, the introduction discusses the ecological perspective of Metaverse, focussing on the people and the developers as well as the way they interact through the platforms.