The optical absorption spectra of cerium (III) and cerium (IV) in Na2O-B2O3, Na2O-SiO2, Na2O-P2O5 glasses, and in H2O-H2SO4 and H2O-H3PO4 solutions have been studied. Individual molar extinction coefficients of cerium (III) and cerium (IV) at different wavelengths (350 to 200 nm) have been estimated. In all the glasses and solutions, cerium (IV) produces a very strong and broad charge transfer band around 250 nm; the intensity, half-width, and position of this band change appreciably with glass composition. Cerium (III) in glass and in aqueous solution produces a number of absorption bands in the ultraviolet region corresponding to the f → d transitions. The cerium (III) bands are sharp and well resolved in Na2O-P2O5 and in low-alkali borate glasses; the sharpness of resolution deteriorates in Na2O-SiO2, and in high-alkali borate glasses. The intensity of cerium (III) absorption also changes with glass composition. In all the glasses the molar extinction coefficient of cerium (IV) is 5 to 10 times stronger than that of cerium (III).