The piezoelectric effect in ferroelectric single crystals and ceramics is investigated considering intrinsic (lattice), and extrinsic (originating mainly from displacement of domain walls) contributions. The focus of the study of intrinsic properties is on piezoelectric anisotropy, which was examined using the Landau-Ginsburg-Devonshire phenomenological theory. It is shown that the enhanced piezoelectric response along nonpolar directions, observed in many perovskite systems, is a consequence of the flattening of the Gibbs free energy profile. This flattening is common for temperature-, composition-, and external field-induced enhancement of the piezoelectric properties along nonpolar axes. A brief review of recent advances in understanding the origins of the piezoelectric nonlinearity, hysteresis, and frequency dispersion is also given.