Studies in the last two decades have firmly established that nitric oxide (NO) exerts a broad range of effects on bodily functions including muscle contractility, platelet aggregation, metabolism, neuronal activity, and immune responses. The underlying mechanisms rely primarily on elevating guanosine 3',5'-cyclic monophosphate due to the stimulation of soluble guanylyl cyclase, inhibiting mitochondria respiration by the action on cytochrome C oxidase, and nitrosylating proteins and enzymes. Under pathophysiological conditions, an increased production of NO concurrently with an enhanced generation of superoxide leads to the formation of peroxynitrite, a potent oxidative agent, and thus tissue injuries. This article intends to provide a brief review on the effects of NO in the modulations of muscle contractility, platelet aggregation, metabolism, neuronal activity, and immune responses. The actions of NO vary depending on the interactions between this gaseous molecule, its derivates, and their effectors as well as the local redox environments. Considering the complexity of these interactions and the widespread presence of NO in various body systems and cell types, there is no doubt that this area of research will remain very challenging and rewarding in the foreseeable future.