Stress relaxation describes how polymers relieve stress under constant strain. Because they are viscoelastic, polymers behave in a nonlinear, non-Hookean fashion. This book presents current research in the study of polymer relaxation, including the secondary relaxations in amorphous polymers; nuclear magnetic resonance relaxation approaches; electrochemical relaxation studies of polythiophenes and dielectric relaxation of onion-like carbon based polymer composites.