Nicotinamide phosphoribosyltransferase Nicotinamide phosphoribosyltransferase (Nampt Nampt ) is a key nicotinamide adenine dinucleotide (NAD) NAD biosynthetic enzyme in mammals, converting nicotinamide nicotinamide into nicotinamide mononucleotide nicotinamide mononucleotide (NMN NMN ), an NAD intermediate. First identified in humans as a cytokine cytokine pre-B-cell colony enhancing factor pre-B cell colony enhancing factor (PBEF PBEF ) and subsequently described as an insulin-mimetic hormone visfatin visfatin , Nampt has recently excited the scientific interest of researchers from diverse fields, including NAD biology, metabolic regulation, and inflammation. As an NAD biosynthetic enzyme, Nampt regulates the activity of NAD-consuming enzymes such as sirtuins sirtuins and influences a variety of metabolic and stress responses. Nampt plays an important role in the regulation of insulin secretion insulin secretion in pancreatic β-cells. Nampt also functions as an immunomodulatory cytokine cytokine and is involved in the regulation of inflammatory responses. This chapter summarizes the various functional aspects of Nampt and discusses its potential roles in diseases, with special focus on type 2 diabetes mellitus (T2DM).