Mucins are the principal organic constituents of mucus, the slimy visco-elastic material that coats all mucosal surfaces. Compelling evidence suggests that they play an integral role in non-immune protection of the oral cavity. Specific protective functions include: 1) protection against desiccation and environmental insult, 2) lubrication, and 3) antimicrobial effects against potential pathogens. Biosynthesis of mucin is regulated by both intrinsic ("cooperative sequential specificity") and extrinsic ("structural modulation") controls. These controls form the basis by which mucin's structure can be modified to meet a dynamically changing biological need.