Ammonia emission to the atmosphere is an important environmental problem. A significant increase in ammonia emission is expected in automotive and energy production sectors in the near future. It is related to the spreading of technologies that use ammonia for NO_x conversion in flue gases (e.g. DeNOx, DEF) and combustion of nitrogen rich fuels (e.g. biogas, biomass). Among the various methods of ammonia elimination from flue gases, its catalytic selective oxidation to dinitrogen seems to be the most promising one. Different types of catalytic systems active in selective ammonia oxidation are presented and discussed. Moreover, the possible mechanisms of ammonia oxidation and the concept of a bifunctional catalyst are discussed and analysed. Finally, future trends in these studies are suggested.