This paper relates experiences of a project where an ethnographic study of air traffic controllers is being used to inform the design of the controllers’ interface to the flight data base. We outline the current UK air traffic control system, dkcuss the ethnographic work we have undertaken studying air traffic control as a cooperative activity, describe some of the difficulties in collaboration between software developers and sociologists and show how the ethnographic studies have influenced the systems design process. Our conclusions are that ethnographic studies are helpful in informing the systems design process and may produce insights which contradict conventional thinking in systems design.