This chapter discusses the frying, baking, and roasting, a thermal process of food preparation. Roasting and baking are cooking in hot air. Although the same basic principles govern both operations, the term baking is usually reserved for dough products, while the term roasting refers to the application of dry heat to all other types of foods, from meats to snacks. Frying, on the other hand, is cooking in fat. As a unit operation, it is quite distinct in the mechanisms involved, its kinetics, its nutritional and safety aspects and the operation principles of the equipment used for its implementation. The primary objective of baking, roasting, and frying is the transformation of foods into products with improved eating quality. At the same time, these processes contribute to the short-term stability of foods by means of two mechanisms: heating and drying. Long-term preservation is usually not expected from these operations, unless they are combined with other preservation methods.