Radiation preservation of food has been raising various questions regarding the possibility that ionizing radiation may induce the formation of toxic, mutagenic, and carcinogenic materials and/or reduce the nutritional value of foods. Whatever products are formed, the knowledge of their absolute yields and the relationship to the dose and conditions under which irradiation is undertaken are integral parts of the overall assessment of the acceptability of radiation treated foods. This chapter briefly reviews radiation chemistry as it pertains to solutions of water soluble food components. Gamma rays from radioactive sources or high energy electrons from machine sources lose energy to the medium by interactions with valence electrons. Radical-radical reactions are the main reactions of secondary free radicals that will take place either under pulse or continuous irradiation conditions. Thus, the basic radiation chemistry kinetics and mechanisms allow us to predict the products. Though similar, the radiation chemistry of amino acids cannot be directly extrapolated to peptides and proteins.