Public food service organizations are large producers of food waste, which leads to greenhouse gas emissions and the waste of natural resources. The aim of the present article was to gain insight into reasons for food waste and possible solutions for lowering food waste in schools in Sweden. In order to do so, food waste quantification in school canteens in two Swedish municipalities and nine qualitative interviews with key actors were conducted. Both municipalities displayed a high degree of variation in food waste, but the common pattern was that serving waste constituted the largest fraction of food waste, followed by plate waste and storage waste, as well as a gradual decrease in food waste over time. Food waste was mainly a result of old, disadvantageous habits, such as overproduction due to forecasting difficulties, whereas new, better routines such as serving fewer options, better planning, and a less stressful environment are the key to lowering food waste. Because food waste varies from one case to the next, it becomes important to identify and measure the causes of food waste in each school in order to be able to establish tailor-made, conscious, and flexible food waste mitigation routines.