The impetus to write this book was based on several recent developments in the field of opioid pharmacology, specifically with regard to the pain-relieving effects of these compounds. A careful review of the existing literature revealed that although some volumes deal with opioid pharmacology in general, no recent books focus on the analgesic actions or integrate basic research with clinical applications. The past several years have seen some extremely exciting research developments that have shed new light on mechanisms of opioid analgesia and have stimulated novel approaches to the treatment of acute and chronic pain. Thus, the aim of this book was to gather a group of internationally renowned experts in basic and clinical aspects of opioid actions in pain control. I am extremely grateful to all the contributors who have made extraordinary efforts to write these overviews of their respective fields. Also, I extend my thanks to the publisher, in particular to Jo-Ann Strangis and to my colleagues in the Department of Anesthesiology at Freie Universität Berlin for their invaluable help. In the end, the spirit for this collaborative effort was fueled by my mentor and one of the most prominent investigators in the field, Albert Herz.