Vanadium oxide or V-containing systems are extensively used as components of various catalysts used in mild oxidation, ammoxidation and dehydrogenation of hydrocarbons and other organic compounds. The discussed examples are the definite phases (V-P-O, butene and butane oxidations), supported bulk and monolayers (V-Ti-O, o-xylene oxidation), and mixed oxides (V-Mo-Nb-O, ethane oxidation). The common structural features are commented. Heteropolyacids, which can be stabilized either on structurally related heteropolysalts or on silica doped with potassium, are also considered as they contain similar molecular sites. The model of coherent interfaces, proposed to explain the synergic effects exhibited by most of these catalysts, is discussed and compared with concepts of other authors.