The spectral dependence of the fundamental absorption edge of congruently grown undoped LiNbO3has been measured from 10 to 667 K. Similar measurements on stoichiometric samples were made at 80 and 300 K. In all cases at all temperatures the edge is broad and featureless and showed very little dichroism (<0.01 eV). The spectral dependence of the absorption is exponential at high temperatures but not at low temperatures. Possible models to explain the observed shapes are discussed.