This chapter deals with mechanistic aspects of the oxidative dehydrogenation of ethane and propane at short contact times over two families of catalysts, i.e. materials based on nonreducible (rare-earth and alkaline-earth) and reducible (vanadia-based) metal oxides. Particular attention is paid to the role of the nature and coverage of surface oxygen species in heterogeneous and homogeneous pathways in the above reactions.