Ascorbic acid, commonly known as vitamin C, is a water-soluble essential nutrient and potent antioxidant that plays critical roles in human physiology including collagen synthesis, immune function, and free radical scavenging. Chemically, it is a six-carbon lactone with enediol functionality enabling its reducing properties. It occurs naturally in citrus fruits, vegetables, and is widely used as a food additive (E300) for preservation and fortification. In food science, it prevents enzymatic browning, acts as a dough improver in baking, and enhances iron absorption. It is unstable in heat, light, and alkaline conditions, readily oxidizing to dehydroascorbic acid. Industrially produced via fermentation or synthesis, it is GRAS by FDA and approved for use in foods globally.