Nitric oxide (NO) is a gasotransmitter involved in various aspects of reproduction. The observational data from different species, such as sea urchin, ascidians, amphibians, rodents, porcine, bovine, and human, suggest that NO might have a significant role in reproduction through several mechanisms. This proposed role might appear preserved through evolution; however, the effects of NO also depend on the species or stages considered. There has been debate over the physiological relevance of NO, though the benefits of its use in assisted reproduction are now widely recognized. Over the past years, S-nitrosylation has provided a new angle to decipher the mechanisms through which NO exerts its actions. This chapter summarizes, in a nonexhaustive manner, research that explores the role of NO in gametes and embryos.