The decision to fly and the capacity to carry a. flight to a successful termination involves a wide spectrum of background determinants. These range from considerations of the pilot as a physical being with specific potentials and limitations of body structure, mental ability and emotional capacities to the adequacy of learning related to a specific performance and the character and condition of the aircraft, Specific factors relevant to each of these categories is discussed including the psycho-social, physiological and pathological. Crucial to success is the pilot's self-critical judgement. There is a necessary tension between the ongoing activity of carrying out a positive decision to fly and the requirements for continual assessment of the situation.