This review provides an in-depth analysis of lanthanide-titania-modified semiconductor photocatalysts (Er-, Ho-, Nd- and Tm-TiO2) for the photocatalytic degradation of organic pollutants under UV and visible light irradiation. In the first section, the unique properties of the lanthanides are summarized. In the second section, the influence of the preparation methods and surface properties of the selected rare earth metals (RE) on the photocatalytic activity of TiO2 was surveyed. In the third section, the mechanism of the RE-TiO2 visible light photoactivity was described. Finally, first-principles computer simulations of the RE-TiO2] structure and energy along with the influence of the anti-Stokes up-conversion process on the photocatalytic activity of the RE-TiO2 were discussed in detail.