Packaging that provides a strong barrier to the passage of gases or moisture is vital for many products. Barrier films, generally manufactured by bonding different films together to form a laminate, are necessary for the packaging high-value perishables with longer storage times, from shelf-stable foods to medicines and vaccines.Permeability is the measure of the ease with which a material can be penetrated by a given gas or liquid. The availability of polymers with low gas permeability has extended the development of barrier packaging materials by providing alternatives to aluminum or metallized films. This article will review the basic requirements of barrier packaging and how the adhesive is critical to the function. This information should provide the adhesive formulator with an understanding of the impact that gas or moisture permeability will have on his or her product. Most often special polymeric films are used as the primary material to "engineer" the degree of permeation desired, and an adhesive is required to assemble a package or a combination of several films to provide optimal properties...