A survey is given of the kinetic theories for polymer solutions and polymer melts, with emphasis on the derivation of constitutive equations. Forsolutionsthe discussion is divided into two parts: (i) the elementary dumbbell models, which provide considerable information about nonlinear rheological behavior without much expenditure of mathematical or computational effort, and (ii) the freely jointed chain models, which are more realistic. Formeltstwo kinds of theories are compared: (i) the older Gaussian network theories, and (ii) the newer reptating chain theories. The most successful constitutive equations now available are those derived by, or at least inspired by, molecular theories.