Polymer composites, along with materials comprising viscoelastic properties are the focus of interest from the viewpoint of developing novel goods and special machinery. Mechanical characteristics of such viscoelastic materials are estimated by quasi-static tests conducted for creep and relaxation. The present monograph covers stress relaxation aspects in viscoelastic materials. Resistance of viscoelastic materials to relaxation under the influence of temperature, deformation, environment, radiation, friction, wear and other operation conditions have been traced. The book has been written primarily keeping in mind engineers, designers, scientific workers, post-graduates and students engaged in experimental and theoretical study of the mechanics of viscoelastic materials.