Nonenzymatic glycosylation of human hemoglobin has recently received increased attention because of its relevance to diabetes mellitus. The reaction of carbohydrates and protein, often called the Maillard reaction, is well known in the food industry. The Maillard reaction is actually a complex scheme of many reactions and is the primary type of nonenzymatic browning that can occur in dehydrated or semimoist foods during storage. This reaction results from reducing compounds, primarily sugars, reacting with proteins, peptides, amino acids, or free amine groups and results in changes in the aesthetic, functional, and nutritional properties of the food in which the reaction occurs. In the present review, no attempt is made to cover all the literature. Rather, attention is given to the various chemical and physical factors that can affect the Maillard reaction in foods. Chemical factors include the type and amount of initial reactant species, pH, water content or water activity, and the presence of substances such as liquid humectants and bisulfite. In addition physical factors such as processing and storage temperature, atmospheric oxygen, and packaging during storage can affect the Maillard reaction in foods.