Origins of piezoelectricity of polymer films are classified into three: (a) internal strain, (b) strain dependence of spontaneous polarization, and (c) embedded charges coupled with mechanical and/or dielectric heterogeneity. Recent work on piezoelectricity of the polyvinylidene fluoride electret, which arises from mechanism (b) and/or (c), is briefly reviewed. A molecular theory of piezoelectricity of uniaxially oriented α-helical polypeptide [mechanism (a)] is described, in which the fluctuation formalism of piezoelectric constant is employed, enabling us to analyse the piezoelectricity on the basis of lattice dynamics taking into account microscopic parameters of structure and the force field of the polymer. The theory gives a satisfactory agreement with experiment in piezoelectric constant. A new technique for simultaneous measurement of spectra of the complex piezoelectric constant in a wide frequency range (0.003–30 Hz) has been developed, using digital data processing. The principle of the technique is described, along with some illustrative results.