Blazars are a subclass of Active Galactic Nuclei with relativistic jets pointing at us. For this reason the highly amplified polarized synchrotron emission from their jets dominates in the optical band. Typically, the electric vector position angle (EVPA) of the optical polarized emission in blazars varies in an erratic way. However, in rare cases the EVPA displays long, smooth and monotonic rotations. Being puzzled by this phenomenon missing a solid theoretical explanation, in 2013 we started an optical polarimetric monitoring program called RoboPol. After several years of operation this project has uncovered several key aspects of polarimetric rotations. The most important of these is that polarization properties of the synchrotron emission in the optical appear to be directly linked with gamma-ray activity. In this talk I present the most significant results of the RoboPol program.