Sulfur dioxide (SO2) is an important and universally permitted food preservative extensively used in the processing and preservation of foods of both plant and animal origin. It is known since ancient times as a sanitizing agent or antiseptic. It gained popularity as a preservative due to its apparent lack of toxicity in mammals. It is used in foods in gaseous or liquid form or as its neutral and acid salts like sulfites, bisulfites, or metabisulfites. SO2 is incorporated in foods for its varied applications as antioxidant, bleaching agent, color fixative, inhibitor of enzymic discolorations, and nonenzymic browning in addition to its antimicrobial effects. Foods that are commonly preserved using SO2 are fruits and vegetables, fruit juices and concentrates, syrups, wines and jams, and to a lesser extent prawns, fish, minced meats, sausages, and mushrooms. Specific antimicrobial effects, factors that influence the antimicrobial efficacy of SO2, levels permitted in various foods, its limitations, and other topics are discussed in detail. The food industry requires the continuous use of SO2 in traditional ways until synergistic combinations have undergone detailed investigations on enhanced safety that can lead to further reduction in its permitted levels.