Any one who doubts the future of aviation should realize the helplessness of the science after the armistice because of the complete lack of international laws to make possible its application in Europe, where it was most highly developed. With men and machines ready, they had to hold to the ground largely because there was in force no treaties assuring them the right to cross frontiers. The broad plans for international routes were held up because aviation itself was so big in its expanse that it could not meet its just fulfilment within national lines. As a result a new law must be written. The law of the air will be one of the most intricate and the most fascinating in the world. It presents problems never before presented and covers a scope paralleled only by the laws of the sea. Very fortunately, however, aerial international law may be written at the very start of the science by a common international standard and practice, thus obviating the greatest part of the divergences which long years of habit have grafted into the maritime laws of the various nations. The slate is clean so that uniformity may be assured in a law which is soon to come into the most vital touch with the daily lives of the nations. Who, for instance, owns the air above the various nations? Obviously the individual landowner has rights, especially as to freedom from damage. The nation also has rights, especially for its protection and for police work. How high, however, does this jurisdiction go? Some assert that a maximum altitude should be set, say five thousand feet, above which the air would be as free as the seas; others that each nation must have unqualified control to the limit of the ether. Then comes the question of passports, customs, registration, safety precautions, and damages. As already shown, the man on the ground is helpless against the airplane which chooses to defy him. People and goods can cross national lines by the air without passports or customs. There will be no main ports of entry as in sea or train commerce, and it is too much to think that any nation can patrol its whole aerial frontier in all its various air strata. Undesirable immigrants or small precious freight can be smuggled in with the greatest ease through the route of the air. Obviously the most elaborate international rules are necessary. Planes must have some method of international registration and license, just as in a more limited sense ships on the seas have what amounts to an international status. Landing-fields must be established and open to foreign planes, each nation providing some kind of reciprocal landing rights to other nations. Arrangements must be made so that if a monkey-wrench drops out of a plane a mile or two up in the air proper damages can be collected. For such things there is to-day but little precedent in law.