In recent years, several developments have made it possible to predict the detailed molecular structure of a polymer based on polymerization conditions and to use this knowledge of the structure to predict rheological properties. In addition, new techniques for using rheological data to infer molecular structure have also been developed. Soon, it will be possible to use this new knowledge to design a molecular structure having prescribed processability and end-product properties, to specify the catalyst and reaction conditions necessary to produce a polymer having this structure, and to use rheology to verify that the structure desired has, in fact, been produced. This book provides a detailed summary of state-of-art methods for measuring rheological properties and relating them to molecular structure.