This chapter aims to give an introduction to the book. We ﬁrst introduce the concept of functional data in Section 1.1. We then present several motivating real functional data sets in Section 1.2. The diﬀerence between classical multivariate data analysis and functional data analysis is brieﬂy discussed in Section 1.3. Section 1.4 gives an overview of the book. The implementation of the methodologies, the options for reading this book, and some bibliographical notes are given in Sections 1.5, 1.6, and 1.7, respectively.