Book excerpt: This book addresses the general aspects of current knowledge of multicomponent transport in hydrophylic and moderately hydrophylic polymers. The first part of the book presents the physical and mathematical models which have been developed in order to predict the behavior of systems consisting of polymer, water and low-molecular solutes. The second half addresses different transport devices for controlled delivery and how the principles reported in the first part could be applied to the regulations of kinetics and the rate of transport of water and solutes. Major applications of polymer systems for controlled release in medicine, agriculture, and in industry are also described.