The book is about the development of muscle atrophy which is caused by denervation, disuse, excessive fasting, aging, and a variety of diseases including heart failure, chronic kidney diseases and cancers. Muscle atrophy reduces life quality and increases morbidity and mortality worldwide. It firstly describes the general aspects of muscle atrophy including characteristics, economic and health burden and the current clinical therapy as well. Secondly, basic aspects of muscle atrophy including composition, structure and function of skeletal muscle, muscle changes response to atrophy and experimental models are summarized. Thirdly, molecular mechanisms of muscle atrophy are overviewed including protein degradation and synthesis pathway, noncoding RNAs, inflammatory signaling, oxidative stress, mitochondria signaling, etc. Fourthly, the pathophysiological mechanisms of muscle atrophy in aging and diseases are highlighted. Finally, diagnosis, treatment strategies, promising agents and future prospects of muscle atrophy would be provided. The book will have a broad readership including scientists, undergraduate and graduate students in medicine and cell biology.