The observation that neuropeptide Y (NPY) is the most abundant peptide present in the mammalian nervous system and the finding that it elicits the most powerful orexigenic signal have led to active investigations of the properties of the NPY family of hormones, including peptide YY (PYY) and pancreatic polypeptide (PP). Nearly two decades of research have led to the identification of several NPY receptor subtypes and the development of useful receptor selective ligands. Moreover, these investigations have imp- cated NPY in the pathophysiology of a number of diseases, including feeding disorders, seizures, memory loss, anxiety, depression, and heart failure. Vigorous efforts are therefore continuing, not only to understand the bioche- cal aspects of NPY actions, but also toward developing NPY-based treatments for a variety of disorders. To facilitate these efforts, it was decided to produce the first handbook on NPY research techniques as part of the Methods in Molecular Biology Series. In compiling Neuropeptide Y Prools, I have gathered contributions on techniques considered critical for the advancement of the NPY field from experts in various disciplines. Each chapter starts with a brief introduction, with Materials and Methods sections following. The latter sections are presented in an easy to follow step-by-step format. The last section of the chapter, Notes, highlights pitfalls and the maneuvers employed to overcome them. This information, not usually disseminated in standard research pub- cations, may prove extremely useful for investigators employing these te- niques in NYP research.