This chapter introduces the various multilayer flexible films and their applications. Currently, various polymers such as PE (polyethylene), PP (polypropylene), PET (polyester), and PS (polystyrene) are used to produce clear films for packaging. While these polymers are commonly used in monolayer format, they are also used in multilayer films produced by coextrusion and/or lamination processes. The first industrially practical polyethylene synthesis was discovered by Eric Fawcett and Reginald Gibson at the ICI works in Northwich, UK in 1933. Subsequent landmarks in polyethylene synthesis have revolved around the development of several types of catalyst that promote ethylene polymerization at more mild temperatures and pressures. The first of these was a chromium trioxide-based catalyst discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum. Until recently, the metallocene systems were the most actively used single-site catalysts for ethylene polymerization. Much effort is currently being exerted on developing new, single-site (so-called postmetallocene) catalysts that may allow greater tuning of the polymer structure than is possible with metallocenes. The dynamics of the industrialized nations post World War II have led to a plethora of applications for many polymers from the mid-20th century continuing into the 21st century. The flexible packaging industry has been one significant part of this engine of growth and adoption for use in many applications has expanded into a global economy, as many newly industrialized nations have become global players in this trade.