PZT is the most commonly used piezoelectric material. In spite of intensive experimental and theoretical studies, no model at the atomic scale has been proposed to explain the large piezoelectric effect in PZT, (d33= 520 pC/N), compared to the low piezoelectric response in the simple end-member lead titanate PbTiO3 with no-Zr (d33= 35 pC/N). X-ray absorption spectroscopy (XAS) appears as the technique of choice not only to clarify the role of Zr, but also to quantify the Zr displacement through the Ferroelectric-Paraelectric (F-P) transition. We clearly show evidence of the polar character of the Zr-atoms in PZT with a Zr-shift which will produce a small polarization. Such an atomic configuration for one type of atoms leads to relatively easy switching, i.e. relatively low electric field to align the Zr-polar atoms, which will create a favorable energetic situation for the cooperative switching of the strongly polar Ti-O dipole and would therefore account for the large piezoelectric effect in PZT1. In mixed B-cation systems of the perovskite ABO3 systems, such local configurations for one type of B cations leads to relatively easy switching giving rise to exceptional ferro/piezoelectric properties. Our recent “in-situ” XAS measurements of the giant piezoelectric effect in PbZn1/3Nb2/3O3 single crystal as a function of electric field confirms that large Zn atoms (small polarization) are easily poled and cooperatively align the strong Nb-O dipoles. 1 PRB 81, 174110 (2010)