The fossil evidence is re-examined to determine the structure of Pteranodon ingens. New measurements include the cross-sections and thickness of the wing bones, the degree and direction of movement of the joints, and the size and position of major tendon and muscle insertions. From this data a reconstruction is made suitable for engineering and aerodynamic analysis. The reconstruction is based largely on Eaton's type specimen, 1175, and has a wing span of 6.95 m. The mass is estimated as 16.6 kg by calculating the volume of each part, making due allowance for the soft parts and cavities. The engineering design of the wing is considered in some detail. The shape deduced from the angles of the joints agrees well with that required for strength and aerodynamic efficiency. The strength of each part has been compared with the loads on it in gliding flight, showing that the structure is extremely well designed; it is strong enough everywhere, but with little unnecessary weight. Wind-tunnel experiments on model heads show that the sagittal crest was primarily a weight-saving device; by balancing the aerodynamic loads on the beak, it allows the neck muscles to be reduced, saving much more than its own weight. The performance of Pteranodon as a glider has been calculated, and compared with birds and manmade gliders. With a sinking speed of only 0.42 m/s at a flying speed of 8 m/s, Pteranodon is a superb low speed soaring aircraft, able to soar in weak thermals, or hill lift in very light winds. With its low stalling speed, it could also land very gently. Powered flight is considered, and it is shown that Pteranodon is just capable of level flight; but it is clearly primarily a glider. The environment in which Pteranodon lived is determined as far as possible from an analysis of the palaeobotany, palaeozoology and palaeoclimatology of the Cretaceous. The evidence points to a warmer and more uniform climate with lighter winds than today. This agrees well with Pteranodon's performance, which is ideally suited to light wind conditions. The mode of life is considered, showing that Pteranodon probably lived on sea cliffs facing the prevailing wind. After landing on the top, it would scrabble forwards (it could neither stand up nor walk) and hang from its hind feet over the edge. From here it could easily launch itself. When flying near the cliff it would soar in the hill lift; when far out at sea it would use the weak thermals generated by convection over the warm sea. Dynamic soaring and slope-soaring over the waves are not possible for such a slow-speed glider. Some consideration is given to methods of feeding, social organization and defence against predators. Finally it is suggested that extinction could have been due to climatic change, particularly an increase in the average wind speed at the end of the Cretaceous.