Plants produce a variety of non-methane volatile organic compounds (NMVOCs) that react with photochemical components of the atmosphere and influence the production of atmospheric oxidants. In this review, the case is made that biogenic NMVOC emissions exert one of the primary controls over regional and global atmospheric chemistry. The diversity of biogenic, reactive organic compounds capable of fueling atmospheric chemistry is immense, including terpenes, alcohols, aldehydes, ketones, and organic acids. Considerable effort has been devoted to the design of models capable of predicting NMVOC emission rates, and thus driving atmospheric chemistry models. Over the past decade, however, what once seemed like promising conceptual connections of NMVOC emissions to fundamental biochemical processes such as photosynthesis, have not been realized; this has delayed the development of mechanistic NMVOC emissions models. Future progress in this area will require new subcellular experimental systems, and the biochemical insight that will accompany these investigations. The past use of existing coupled biogenic emission—photochemistry models at the global scale, even with their mechanistic limitations, has revealed the potential for NMVOC emissions from terrestrial ecosystems to cause reductions in tropospheric hydroxyl radical concentration and increases in the concentration and lifetime of radiatively important trace gases such as methane and ozone.