Nitric oxide (NO) is an endogenic product from plants, bacteria, and animal cells that has many important effects in those organisms. It is produced by nitric oxide synthase (NOS), which is found in main three isoforms, namely endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS). It has an important role in homeostasis in different physiological systems, such as micro-and macro-vascularization, inhibition of platelet aggregation, and neurotransmission regulation in the central nervous, gastrointestinal, respiratory, and genitourinary systems. However, its overproduction has been associated with diseases such as arthritis, asthma, cerebral ischemia, Parkinson's disease, neurodegeneration, and seizures. For this reason, and due to better understanding of the molecular mechanisms by which NO provokes those diseases, the interest on the design of NOS inhibitors with therapeutic purposes has highly increased. Based on the foregoing considerations, the proposal of this chapter is to show an overview about the design strategies, mechanism of action at the molecular level, and the main advances toward the search for selective NOS inhibitors available in the literature.