With over 300 references, this book explains the essential aspects of automatic music emotion recognition (MER), including background, key techniques, and applications. It reviews of existing work in the field and establishes a computational framework that generalizes emotion recognition from categorical domain to real-valued 2D space. Furthermore, it describes how to take the subjective nature of emotion perception into account in the development of automatic MER systems. This book can be used as a reference and guide to develop an automatic music emotion recognition system.