The present chapter is intended as a lightweight introduction to ubiquitous computing as a whole, in preparation for the more specific book parts and chapters that cover selected aspects. This chapter thus assumes the preface of this book to be prior knowledge. In the following, a brief history of ubiquitous computing (UC) is given first, concentrating on selected facts considered as necessary background for understanding the rest of the book. Some terms and a few important standards are subsequently mentioned that are considered necessary for understanding related literature. For traditional standards like those widespread in the computer networks world, at least superficial knowledge must be assumed since their coverage is impractical for a field with such diverse roots as UC. In the last part of this chapter, we will discuss two kinds of reference architectures, explain why they are important for the furthering of Ubiquitous Computing and for the reader’s understanding, and briefly sketch a few of these architectures by way of example.