It has become increasingly evident that there is much to begained from a detailed understanding of the structure and properties of polymers in the oriented state. This book reftects the growth of interest in this area of polymer scienceand attempts to give the reader an up to date viewofthe present position. The individual chapters are for the most part self- contained, and cover a very wide range of topics. It is intended that each of them should serve the dual purpose of an expository introduction to the subject and a topical review of recent research. It is inevitable that there will be differences of style and approach in the contributions from the different authors. No atternpt has been made to moderate these differences, as they serve to illustrate the diversity of approaches required to give the reader a balanced view of the subject. I should like to thank the contributors for their endeavours, and especially for their patience in accepting modifications and corrections which make for consistency in the book as a whole. 1 am particularly indebted to Professor Leslie Holliday who originally approached me with the proposition that such a book would be a worthwhile venture and to the publishers who have given me every assistance in making its progress as painless as possible.