On behalf of the Planck collaboration, we will show the tightest constraints on cosmic reionization extracted from the CMB polarization at low multipole by Planck. The CMB large scales polarization data can gives strong constraints on the reionization history through the measurement of the reionization optical depth. The Thomson optical depth measured is significantly smaller than previously estimated from CMB polarization data. This result reduces the tension between CMB based analyses and constraints from other astrophysical sources. It highlights the necessity of a deep revision of our view on the history of reionization and the dark age. We also combine constraints from low and high l, in particular from the amplitude of the kinetic Sunyaev Zeld’ovitch effect (kSZ), to derive the time and duration of the reionization epoch. In addition, using both a new two-stage parametrization of the ionization fraction, closer to recent self-regulated simulations, and a non parametric reconstruction, we estimate a more realistic beginning, end, and duration of Reionization.