The volume sets forth the basic principles and the clinical practice of psychology as a true science of medical psychology and mental disorders. This book is to be viewed benefit from a better understanding of the causes of behavior as we go through life trying to make sense of our own behavior. In Section I ， which is written by Pan Yuanqing， it is focused on simply enhancing the quality of life and our ability to function in a wide variety of circumstances （education， work， relationships， etc.）. We will explore what psychology is， how psychology originated as a science， what clinical psychologists do， and what contents do medical psychology study. In Section n ， which is written by Liang Haiqian， it aims to understanding how can we distinguish normal from abnormal behavior， what are the major perspectives on mental disorders used by mental health professionals. In Section 11 ， it introduces a wide range of mental disorders， covering epidemiology， clinical features， and both psychosocial and somatic therapies.