The application of Tobolsky's time‐temperature superposition principle for the stress‐relaxation behavior of amorphous polymers is reviewed, and its extension to crystalline polymers and the employment of X‐ray and optical methods is discussed. The desirability of applying the superposition principle to time‐dependent crystal orientation functions is described. The use of those techniques for the study of the relaxation of a low‐density polyethylene sample is illustrated. Spherulite orientation theory is used for analysis of the results.