Gas turbines and gas-steam combined plants are presented in this chapter. Their valuable characteristics in the wide field of thermal power plants are the high power-to-weight ratio, the low emissions (CO2, SOx, NOx and particulate), the not high capital cost, the relatively high load variation rapidity, especially for simple cycle turbine engines, the very high efficiency for combined cycles (big plants’ efficiency exceeds 60%). Some important improvements are expected in the future: the use of new materials and cooling techniques, which will allow further increase of the gas temperature at the turbine inlet, the decrease of emissions and the possibility of using alternative fuels; in addition, great attention will be devoted to the improvement of operational flexibility, in order to better comply with the new requirements of the energy market.