This paper reviews the preparation techniques, characterization, and use of nickel molybdate catalysts in the selective oxidation of hydrocarbons, particularly of light alkanes. Catalysts with different Ni: Mo ratios, unsupported and supported, undoped and doped, were considered. Particular attention is given to the thermal activation process for the transition of the low temperature alpha-phase into the metastable beta-phase, which was shown to be more selective in some cases. Special reference is also made to the results of kinetic studies performed, to the mechanisms proposed for some important reactions, and to the nature of the active sites. Finally, after some general conclusions, future trends are analyzed.