The present book is a sequel to "Elastomers and Rubber Elasticity," edited by J.E. Mark and J. Lal and published by the American Chemical Society in 1982. It is also based on papers presented at an ACS Symposium, sponsored by the Division of Polymer Chemistry, Inc., in this case one held in Chicago in September of 1985. The keynote speaker was to have been Pro­ fessor Paul J. Flory, and his untimely death just prior to the symposium was a tremendous loss to all of polymer science, in particular to those in­ terested in elastomeric materials. It is to his memory that this book is dedicated. There has been a great deal of progress in preparing and studying elas­ tomers since the preceding symposium, which was in 1981. In the case of the synthesis and curing of elastomers, much of the background necessary to an appreciation of these advances is given in the first, introductory chapter.