The cuticle is the outermost layer, deposited on the palisade layer of the eggshell during the last 1.5-2 hr of eggshell formation in 'utero'. It is a non-calcified, thin, water-insoluble layer composed mainly of glycoproteins with some carbohydrate and fat constituents. The cuticle functions as a protective layer which regulates gaseous exchange across the shell, acts as a first line of defence against microbial penetration across the eggshell and is associated with termination of calcite crystal growth during shell formation. The extent of cuticle deposition is influenced by hen age and strain. The physiological and microbiological characteristics of the hen eggshell cuticle are reviewed in relation to its protective functions.