This paper describes an investigation on the combined influence of environment and temperature on the tribological behaviour of a carbon-carbon (C/C) composite material with a particular reference to the interaction between water vapour and oxygen in air and the carbon surface. Experiments were conducted in nitrogen and air with a low-speed three-pins-on-disc apparatus and a high-energy ring-on-ring apparatus. Like conventional graphitic carbon materials, C/C composites exhibited a high friction and wear phenomenon, also known as "dusting", in dry nitrogen from room temperature up to 700 degrees C owing to the lack of lubricant gases and vapours in the environment. In ambient air, however, C/C composites exhibited three temperature-dependent tribological regimes. Abrupt increases in the friction at 150-200 degrees C and 650-700 degrees C marked the transitions between different regimes. The transition phenomena were explained in terms of the desorption of physisorbed water vapour and chemisorbed oxygen from the rubbing surface.