for border control formalities, of air traffic flowing between these States. Pre-clearance is intended to streamline border procedures, to reduce congestion at ports of entry, and to facilitate travel between the points of departure and destination. The pre-clearance facilities that exist for air travel between Canada and the United States are a well-known example of such arrangements between States. Canada has allowed United States Federal Inspection Services to operate air passenger pre-clearance in Canada since the 1950s, for traffic beginning its journey in Canada and seeking entry into the United States.