Impatience is frequently expressed at the slow rate of progress in improving the efficiency of air traffic control. It is being expressed most forcibly at this time in the United States, because the military services require the separation problem to be solved for the large numbers of military jet flights, and because civil jet aeroplanes have been ordered by the airlines and will soon appear on the Federal Airways. Although a great deal of basic study has been made of the problem of air traffic control, it is becoming clear that there is no panacea for its solution. Air traffic control is concerned with the safe expeditious flow of air traffic. This involves a number of separate but interrelated problems both in the aircraft and on the ground. Thus we see a programme of development on a very wide front involving navigation aids, communications, radar performance and presentation, data display and so on. Progress in any one field may affect the requirements in another, and so it is most necessary for all concerned to have a clear view of the situation as a whole in order that they may see the wood as well as the trees. Lively discussion of the subject can therefore be most fruitful, both among those directly concerned—the pilots and the controllers—and among the specialists in the various branches of development.