As the first coenzyme discovered over a century ago, NAD+ (nicotinamide adenine dinucleotide) was found in all living cells from single-celled microorganism, such as bacteria and yeast, to mammals, such as animals and human. It is ubiquitous in all human tissues. Hundreds of very important biological activities in the human body require the participation of NAD+. It is an essential coenzyme to metabolize carbohydrates, fats, and proteins from our diet into energy and other essential nutrients. In addition, it plays an important role in many important biological pathways, such as DNA repair, gene expression, etc. However, NAD+ level decreases significantly during aging. Declining NAD+ level in the human body accelerates aging and contributes to many age-related diseases, such as muscle loss, cardiovascular diseases, neurodegenerative diseases, etc. Replenishing NAD+ has shown to slow the aging process and ameliorate age-related symptoms. NAD+ levels have significant impact on all twelve hallmarks of aging. NR (nicotinamide riboside) and NMN (nicotinamide mononucleotide) are two important NAD+ precursors that effectively raise NAD+ level in both animal studies and human clinical trials. Extensive research has been done during recent years on NR and NMN as NAD+ precursors for their effect and biological mechanism of health and longevity. The dietary supplements of NR and NMN have been commercially available in several countries since 2013. In this chapter, we will give a historical review and current status of NR and NMN as nutritional supplementations on human health and longevity.