In recent years the study of nicotinamide adenine dinucleotide (NAD) biochemistry has been the focus of attention for many researchers. Although the role of NAD in cellular metabolism and in redox reactions had been recognized for over a century, it was also during these recent studies that the precise identification of all NAD biosynthetic routes was achieved and that the variety of NAD controlled cellular processes began to emerge. Being vital not only for energy transduction, but also for intracellular signaling pathways, this pyridine nucleotide can be considered the most important link between energetic and regulatory processes. The control of such important events suggested NAD as a possible therapeutic target for the control of different pathological states, including metabolic disorders and neoplastic transformation. This review briefly summarizes the recent advances achieved in this field.