Mucins produced by corneal and conjunctival epithelia, conjunctival goblet cells and lacrimal apparatus are important components of preocular tear film, which play important roles as clearing molecules, lubricating agents, antimicrobial agents, dis-adhesive molecules, protective cell surface barrier, osmosensors and signal transmitter. The understanding of the functional roles of mucins and the regulatory steps governing its synthesis and secretion is necessary to develop effective treatment strategies for dry eye.