The objectives of flue-curing tobacco are to maintain and enhance the potential quality embodied in the harvested leaf and to provide an environment conducive to the transformation of that leaf into a high quality cured tobacco product. This is achieved through control of the chemical and biochemical conversions and moisture removal that take place during curing. The flue-curing of tobacco typically takes place over a period of five to seven days compared to one to two months for air-curing. The process is divided into three stages: yellowing (35-40°C) for 48-72 hours, leaf drying (40-57° C) for 48 hours, and midrib (stem) drying (57-75°C) for 48 hours. Most of the major chemical and biochemical changes begin during the yellowing stage and continue through the early phases of leaf drying. The rates of chemical change and moisture removal are controlled by varying time, air temperature, relative humidity, and air velocity in the curing barn. Important changes that occur during the flue-curing of tobacco include chlorophyll degradation and the concomitant revelation of the yellow carotenoid pigments, hydrolysis of starch to free sugars and partial respiration of those sugars to carbon dioxide, hydrolysis of proteins into free amino acids and subsequent reaction of the free amino acids with free sugars to form Amadori compounds, variable changes in polyphenols, the thermal degradation of leaf surface diterpenes and sugar esters into more volatile constituents, and the conversion of nitrate into nitrite and its subsequent reaction with tobacco alkaloids to form tobacco specific nitrosamines. Many of these changes result in the production of compounds characteristic of the flavor and aroma of flue-cured tobacco. This review discusses the chemical and biochemical changes that occur during flue-curing and the effect of altered curing regimes on the chemistry and quality of the cured leaf.