The core of Active Galactic Nuclei (AGN) remains under the resolution limit of the vast majority of current telescopes. However, polarimetry provide us with information of those unresolved regions, which would be inaccessible in natural light, such as the presence of dust, magnetic fields or scattering regions. This talk will be focused on the optical polarization properties of radio-quiet AGN and its relation with the geometry of the scattering regions, which in turn configures the AGN structure of the innermost regions. Actually, polarized light was the key to establish, more than 30 years ago, the Unified Model of AGN. Nowadays, polarization can help us to disentangle some observational facts challenging that classification scheme, as for instance changing-look AGN.