Airport systems exist in the context of their major clients, the airlines. To build airport facilities that will perform effectively over the 30 to 50 years of their lifetime, it is necessary to appreciate this context. Understanding the state of the airport/airline industry in the early twenty-first century gives a perspective on its future. This is the starting point for a forward-looking text on airport systems planning.Three trends dominate the airport/airline industry in the early twenty-first century: Long-term growth