This revised second edition of the book discusses new developments regarding understanding the causes of pain and its different treatments; the book explains the bases for many forms of treatment and management of pain and it discusses how effective different pain treatments are and the risk of side effects of many conventional treatments are discussed in detail including the importance of how treatments such as medications are administered. The second edition of this book on pain discusses many aspects of pain such as how pain can affect people, the cause and the treatment of many forms of pain including some new little known new treatments. Other parts of the book discusses little known effects of inflammation and the role of the immune system in many forms of pain including low back pain. The book provides a multidisciplinary, comprehensive, and broad coverage of up-to-date knowledge about the anatomical and physiological bases for many forms of pain. The role of neuroplasticity in many forms of pain is discussed. The main types of pain -- pain that is caused by stimulation of pain receptors in normal tissue (physiological pain) and pain that is caused by pathological processes and change in the function of the spinal cord and the brain (pathological pain)-- are discussed in separate Sections. The book is suitable for anybody interested in pain; a person who has pain will find information that may relate to his/her own pain. Pain is complex; it can be an adverse phenomenon that deserves treatment, but at the same time, some forms of pain are absolutely necessary for a normal life. Pain is a fascinating yet frightening subject, from wherever and however it is viewed. It has emotional features and medical features. Pain can last a short time (acute pain) or it can last a long time (chronic pain). Understanding pain and its cause is both interesting and challenging. Pain is a self-experience, it cannot be measured and it cannot be seen or evaluated on MRI scans. Many people are afraid of pain; some are afraid of dying because they believe it will be painful. Pain in itself is not life threatening (except when it cases a person to commit suicide), but it decreases the quality of life. Some forms of pain may give pleasure to some individuals; it may have a role in sexual behavior. Some individuals with some diseases, such as autism, have an abnormal perception of pain. There are ample treatments available for acute pain but treatment of chronic pain and pain of no known cause, especially, is challenging, but rewarding. Pain is not a sense like hearing and vision. Pain may be a symptom of a disease or a physical trauma, but the cause of many forms of pain is unknown. Pain plays an important role in diagnosis of many diseases but a patient's description of his/her pain can be complex and difficult to interpret. The book is derived from my many years of teaching both undergraduate and graduate courses on the “Biology of Pain” in the Neuroscience Program of the School of Behavioral and Brain Sciences at The University of Texas at Dallas. I still use the book as a text for my course.