This book deals with three related areas having both fundamental and technological interest. In the first part, the objective is to provide a bird's­ eye view on structure in polymeric solids. This is then complemented by a chapter, directly technological in its emphasis, dealing with the influence of processing on polymeric materials. In spite of the technological interest, this leads to some of the current fundamental theory. Part II, concerned with liquid crystals, starts with a discussion of the physics of the various types of material, and concludes with a treatment of optical applications. Again, aspects of the theory are stressed though this part is basically phenomenological in character. In Part III, an account is given first of the use of chemical-bonding arguments in understanding the electronic structure of low-dimensional solids, followed by a comprehensive treatment of the influence of dimen­ sionality on phase transitions. A brief summary of dielectric screening in low-dimensional solids follows. Space-charge layers are then treated, including semiconductor inversion layers. Effects of limited dimensionality on superconductivity are also emphasized. Part IV concludes the volume with two specialized topics: electronic structure of biopolymers, and topological defects and disordered systems. The Editors wish to acknowledge that this book had its origins in the material presented at a course organized by the International Centre for Theoretical Physics, Trieste.