AbstractMechanical and dielectric relaxations in crystalline phase (crystalline relaxation), glassy phase (local mode relaxation), and paracrystalline phase (paracrystalline relaxation) are interpreted in terms of torsional motion of chains in respective phases. A theory is developed on the relaxation strength, and a satisfactory agreement is found between theory and experiment for mechanical crystalline relaxations in normal paraffins. Dielectric crystalline relaxations in oxidized paraffins, poly(vinyl alcohol), and polyoxymethylene, dielectric paracrystalline relaxation in polyacrylonitrile, and local mode relaxations in several polymers are studied both experimentally and theoretically.