D-Galactose is a monosaccharide sugar that serves as an energy source and glycosylation component. It is a C-4 epimer of glucose and often used as a source of carbon in culture media. Galactose is a component of the disaccharide lactose and released upon hydrolysis by β-galactosidase enzymes. It is converted to glucose via the Leloir pathway or metabolized via an alternative pathway, such as the DeLey-Doudoroff pathway.

D-Galactose is a monosaccharide sugar typically abbreviated Gal. This specific form of D-Galactose is derived from peach gum which is important when making recombinant proteins for therapeutic purposes in order to avoid animal diseases like Bovine Spongiform Encephalopathy.