The dehydrogenation of alkanes over supported chromium oxide catalysts in the absence of oxygen is of high interest for the industrial production of propene and isobutene. In this review, a critical overview is given of the current knowledge nowadays available about chromium-based dehydrogenation catalysts, in particularly the industrially used Cr/Al2O3 catalysts. It will be shown that detailed information on the dehydrogenation site can be obtained by using advanced spectroscopic tools.