It has been claimed that music is one of the finest languages of emotion [252]. The relationship between music and emotion has been studied by researchers from several disciplines. Many researchers have suggested that music is an excellent medium for studying emotion, because people tend to make judgments about music and their affective responses to music [102,159]. The purpose of this chapter is to provide an overview of the techniques developed for emotion description and emotion recognition. Specifically, this chapter is divided into two parts. The first part discusses the emotion models that have been proposed by psychologists, so that the readers can get a sense of how emotions are usually conceptualized. The second part describes some well-known work on MER and provides the details of the basic components of an MER system. The concepts introduced in this chapter are important to the understanding of the remaining chapters of the book.