Transmission electron microscope studies of Ti‐doped, congruent lithium niobate (LiNbO3) have shown that extended structural faults are only present within the Ti‐diffused layer (i.e., the wave guiding region). Structural faults have also been observed in undoped Li‐deficient LiNbO3, though not in undoped control crystals of congruent and stoichiometric LiNbO3. In both Ti‐doped and Li‐deficient LiNbO3, crystal chemistry predicts an increase in the concentration of the point defects V’’’’’Nband Nb....Liand therefore it is appealing to suggest that these defects are responsible for the creation of structural faults. Since the extent of these structural faults is tens of microns, they are clearly potential scattering sites for photons. In this regard, a systematic understanding of their origin and thermal stability is crucial to integrated optical device technologies based on LiNbO3and on the Ti‐doped waveguide fabrication technique.