This introductory chapter provides an overview of the papers presented at the symposium on Barrier Polymers and Barrier Structures that was sponsored by the Polymer Chemistry Division of the American Chemical Society at the Spring 1989 meeting. A total of nineteen papers from the symposium are included in this volume. Topics covered include barrier transport fundamentals, advanced composite structures, reactive surface treatments and the effects of orientation on barrier properties. Relationships between polymer molecular structure and barrier efficacy are also treated in detail. Time and history dependent phenomena associated with retorting of barrier laminates are discussed from the standpoint of theoretical modeling and experimental characterization of the barrier layers. The effects of concentration dependent diffusion, flavor scalping and nonFickian transport phenomena are also discussed. The coverage, therefore, is broad while providing sufficient depth to provide a state-of-the-art update on the major technical issues facing the barrier packaging field.The development of efficient packaging materials and containers has allowed the evolution of the modern market system based on concentrated production facilities supplying individuals residing far from the ultimate source of products. The goal of the packaging industry has been to provide increasingly more cost effective means of preserving the quality of materials with as close to their as-produced natures as possible.Modern packaging is a sophisticated technology rooted deeply in fundamental polymer science. Nevertheless, the sheer size and competitiveness of the packaging industry also makes it an extremely practical field with an eye to applying polymer science to achieve the bottom line of cost and barrier efficiency. This book seeks to BARRIER POLYMERS AND STRUCTURESreflect the dual nature of this technology by presenting fundamental principles along with complementing discussions of applications of these principles by leaders in the field.Many excellent reviews of the fundamental processes by which small molecules penetrate between the segments comprising a polymeric film are available (1-10). These reviews, coupled with past symposia publications related to barriers and the allied field of membranes (11-18) should allow a newcomer to the field to rapidly gain the needed background to become an active participant in this dynamic technology.The chapters in the present book reflect the current research and development directions of active university and industrial participants in the barrier field.The overview provided by this first chapter gives a framework for appreciating the more detailed subsequent discussion of topics that are at the cutting edge of this evolving technology. Therefore, it is anticipated that this book will be of interest to both the current expert and the newcomer to the field. FundamentalsIn addition to providing a container to prevent scattering and bulk phase mixing of components, modern packages control the exchange of compo...