The main objective of catalytic combustion is to attain a flame temperature 300-400 Klower than in thermal or non-catalyzed combustion; this substantially reduces the direct combination of nitrogen and oxygen in air to form the so-called thermal NOx. In this way, catalytic combustion is a preventive solution to the problem of nitrogen oxides emissions. The focus of attention here is its application in gas turbines, both for power production and for transportation by road, sea and air. Any catalyst for catalytic combustion, however, has to face extreme demands: continuous operation above 1000 degreesC in the presence of oxygen and steam for preferably 30,000 h, resistance to poisons in the fuel and/or process air, and ability to withstand large thermal and mechanical shocks. While material/catalyst advances are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid reactors. The deactivation of catalyst supports, washcoats, and active materials is briefly reviewed here: sintering, vaporization, phase transformation, thermal shock and poisoning.