Nitric oxide is a persistent radical which results from the direct combination of nitrogen and oxygen. While it has a long standing history, it is still of considerable chemical and biological importance. More recently, research efforts have been reinvigorated by efforts to control NO emissions from internal combustion engines (especially with the advent of alternative fuels) and to understand its functional role in biology. NO has indeed been identified as a key physiological regulator involved in a variety of biological processes. An important factor in the chemistry of NO and NO2 is the strength and prevalence of van der Waals complex formation, especially their self and cross dimers.