This chapter presents various definitions of food additives provided by food safety law, Codex Alimentarius, European Union, United States, and Japan. Food additives generally have the following characteristics, they are the substances added to food and cannot be consumed alone as food themselves, they include synthetic substances as well as natural substances and the purpose of addition is to improve the quality, color, fragrance, flavor of food, and to meet the demands of preservation, freshness and processing. The chapter explains the functional classification and effects of food additives, principles for the use of food additives and the effects of food additives in the modern food industry. In order to standardize the use of food additives, the Joint Expert Committee on Food Additives (JECFA) and the Codex Committee on Food Additives (CCFA) were established internationally in 1955 and 1962, respectively. Finally, the chapter talks about the development trend of food additives in the future.