The surface structure and the oxidation state of chromia catalysts supported on titania are investigated by vibrational spectroscopy, UV-visible diffuse reflectance measurements, and X-ray photoelectron spectroscopy (XPS). Pronounced changes are observed as the chromia loading is varied between 0.5 and 30 wt%. While isolated surface-bound chromate ions prevail at low coverages, an increasing fraction of trimeric and tetrameric clusters, as well as of higher aggregates, is observed for chromia contents ≥10 wt%. On the 0.5% CrO x /TiO 2 catalyst, chromia species in a formal oxidation state of V represent the most abundant surface species, with a significant contribution of Cr (VI). As the chromia coverage is increased, the fraction of Cr(V) is found to decrease, while a growing contribution from Cr(III)/Cr(IV) species is detected. In situ calcination studies show that the temperature of conversion of the Cr(NO 3) 3 precursor (deposited by incipient wetness impregnation) into the oxidized surface chromate species depends on coverage. With 3 wt% chromia content, coordinatively unsaturated surface chromyl species are observed to develop around 373 K, whereas for 30 wt% chromia coverage, conversion into coordinatively saturated surface chromyl species takes place around 413 K. Laser Raman experiments show that the surface chromia supported on titania does not undergo laser-induced crystallisation under the conditions used.