Frying is a unit operation in which food is heated in oil to alter its eating quality. The chapter first reviews principles of heat and mass transfer in frying, followed by a description of the equipment used for contact frying and deep-fat frying, and methods to reduce energy consumption and environmental pollution. The criteria for selection of frying oils are described, together with the effects of frying on oil quality. Finally, there is a discussion of the effect of frying on sensory characteristics of foods, changes to their nutritional value, and health concerns over fried foods and methods to reduce their fat contents.