The enormous size of polymer molecules causes their molecular motions to span a broad range of length scales and give rise to viscoelastic behaviour. This rate-dependence of the properties is a predominant characteristic of soft materials (rubbers, biopolymers, lubricants, adhesives, etc.). Improving the performance and developing new applications for soft materials require an understanding of the basic principles of how molecular motions underlie physical properties. This text is intended to provide grounding in fundamental aspects of the dynamic behavior of rubbery materials, adopting a molecular perspective in its treatment to emphasize how microscopic processes are connected to the observed macroscopic behavior. The latest discoveries and advances in the science and technology of rubbery materials are described and critically analyzed.