Abstract This chapter focuses on the underlying chemistry that takes place in cold or nonthermal plasma. First, the primary electron-induced collision processes are identified for oxygen-nitrogen mixtures mainly at atmospheric pressure. Then the chemistry initiated by the species from these processes is described for the production of nitrogen oxides and ozone. Three case studies of relevance in food and agriculture are presented to demonstrate the development of appropriate chemical mechanisms. These are ozone production, nitrogen fixation, and the removal of volatile organic compounds by plasma.