The aim of this book is not only to introduce readers with a broad spectrum of biological actions of the NOP receptor, but also to feature a detailed look at the N/OFQ-NOP receptor system, medicinal chemistry, pharmacology, and clinical data of NOP-targeted ligands. This special volume book - for the first time focusing on the NOP receptor - is designed to serve as a useful reference, stimulate more research on the N/OFQ-NOP receptor system, and lead to more development of NOP-related ligands for several therapeutic applications.