This paper addresses the combustion behaviour and emission characteristics, under current and projected future operating conditions, of gas turbines fired with natural gas and a range of alternative process gases, including gasification product gas. State-of-the-art gas-turbine designs are currently able to burn natural gas and a range of alternative gaseous fuels efficiently, and meet legislation with respect to emissions of NOx, CO and unburned hydrocarbons. Future demands for increased turbine-inlet gas temperatures and higher operating pressures will dictate that the gas-turbine combustor will operate under conditions significantly removed from current practice, with generally unknown effects on flame stability, combustion efficiency and emission levels. This paper reviews these areas in the light of information available in the literature. Future developments in gas-turbine technology are also discussed, and outstanding research areas are identified.