Rheology is the science and technology that deals with the deformation of polymeric or plastic materials. In this monograph the field of polymer rheology is explained with emphasis on the chemical theory. The book provides basic information on rheology for nonspecialists and gives clear explanations of the various phenomena. The author has developed a new theory of thermodynamics and kinetics using a model of multi-size pseudo crosslinks that provides a comprehensive principle to show how links in chain molecules affect the melting temperatures and determine polymer properties such as viscoelasticity, melt viscosity and elastic and plastic behaviour of bulk polymers. The theory can be extended to include the strength of rubber and plastics, active fillers and adhesion, friction and abrasion.