This chapter introduces the state-of-the-art in research and industry in the areas relevant to this book. In addition, related work is introduced. The chapter is structured as follows. Section 2.1 introduces the foundations of the modeling area, including conceptual modeling, enterprise modeling, and metamodeling. Section 2.2 presents the foundations for extended reality. This includes introductions to virtual reality, augmented reality, and the metaverse, as well as some distinctions of the different technologies in the context of this work. Section 2.3 discusses related work by showing the finding of a comprehensive literature analysis.