The significance of food waste (FW) arises from its large environmental, economic and social impacts. Furthermore, it affects food security and is a matter of resource efficiency for sustainable food production. In a situation where the world population is growing and climate change is affecting food production, FW should be minimized, to ensure the future food supply and natural habitats. The aim of this thesis was to study FW in the Finnish food supply chain, in households, food services, the food industry and the retail sector. Even though FW is generated throughout the supply chain, the impacts are most significant at the end of the chain. That is why reducing FW in households and food services is especially important. In this thesis, FW amounts and types were studied in the food chain in addition to methods for measuring FW and means for reducing FW in households and food services. The definition of FW in this thesis included all originally edible food material but not originally inedible material, e.g. coffee grounds. Diary studies were used for studying the FW in households and food services and in the retail and food industry sector surveys and interviews were used. Together 380 of households from different areas in Finland finished the two weeks study period. The amount, type and origin of avoidable food waste were investigated in 51 food service outlets, including schools, day-care centres, workplace canteens, cafes and petrol stations, restaurants and diners. The average annual FW was about 23 kg per person and 4–5% of the purchased food amount. The main discarded foodstuffs were vegetables (19%), home cooked food (18%) and milk products (15%). The main reasons for disposing of foodstuffs were spoilage, expiry of the best-before or use-by date and plate leftovers. Almost half of the food waste (40%) was still unspoiled at the time of discarding it. In food services the amount of FW varied depending on the outlet type and was about one-fifth of all food handled and prepared in the outlets. During the study period the most FW were generated in day-care centres (28%) and workplace and student canteens (25%). The findings also suggest that the significant origin of FW was serving waste because of food overproduction for buffet lines. In the retail sector about 65–75 million kilograms of FW is produced annually, which is about 1–2 % of the total sales in the sector. In the food industry 75–140 million kilograms of edible food was wasted, this corresponds to roughly 3% of the total production volume of the industry sectors included in the study. According to the results, the total amount of FW in Finland was about 385–485 million of kilograms in a year corresponding to about 15% of the food consumed in Finland. Suitable and appropriate measurement methods for monitoring FW are necessary for reducing FW amounts and following trends in FW. The most suitable method varies depending the sector and the data requirements. Besides FW data, also data about the food purchased or produced is needed for analyses and discussion. The best options to make estimations about the amount of FW in households would be a combination of composition analysis and diary studies as they would provide appropriate data, e.g. the amount of total FW, edible and inedible FW, types of FW, reasons for FW and background data. In food services a suitable method must be simple and easy enough for the personnel to carry out daily, the method needs to provide data about the food produced, the number of customers and the origin of FW.