Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the first reversible step in NAD biosynthesis and nicotinamide (NAM) salvage. The enzyme is designed for efficient capture of nicotinamide by coupling of ATP hydrolysis to assist in extraordinary NAM binding affinity and formation of nicotinamide mononucleotide (NMN). NAMPT provides the mechanism to replenish the NAD pool in human metabolism. In addition to its role in redox biochemistry, NAD fuels the sirtuins (SIRTs) to regulate transcription factors involved in pathways linked to inflammation, diabetes and lifespan. NAMPT-mediated lifespan expansion has caused a focus on the catalytic mechanism, regulation and inhibition of NAMPT. Structural, mechanistic and inhibitor design all contribute to a developing but yet incomplete story of NAMPT function. Although the first generation of NAMPT inhibitors has entered clinical trials, disappointing outcomes suggest more powerful and specific inhibitors will be needed. Understanding the ATP-linked mechanism of NAMPT and the catalytic site machinery may permit the design of improved NAMPT inhibitors as more efficient drugs against cancer.