Recent progress in improvement of the piezoelectric activity in ferroelectric polymers of technical importance is reviewed with relation to manufacturing process of polarized films. The polymers described are PVDF (polyvinylidene fluoride), P(VDF–TrFfE) (copolymers of vinylidene fluoride and trifluoroethylene), P(VDF–TeFE) (copolymers of vinylidene fluoride and tetrafluoroethylene), and P(VDCN–VAc) (copolymer of vinylidene cyanide and vinylacetate). To increase the piezoelectric activity it is most important to enhance crystallinity and orientation of the polar axis in the thickness direction of the film. This is realized in P(VDF–TrFE) with VDF molar content of 60–85%. The maximum electromechanical coupling factor for thickness extensional mode attains about 0.3 in these copolymers.