LiNbO3 is a relevant material to prepare a number of electrooptic (bulk and waveguide) devices. Moreover, its photorefractive (PR) behavior is also potentially useful for optoelectronic applications such as holographic storage and coherent optical amplification. For a full understanding and optimization of the PR effect, the lattice location and valence state of the active impurities is essential, since they determine the ionization and trapping capabilities for free carriers. So far, the information obtained with spectroscopic techniques (EPR, ENDOR, Mossbauer, optical) is not conclusive, except manganese and possible iron.