We are all born, it seems, with an natural curiosity – with an urge to travel. What normal infant, confined to crib or playpen, doesn't soon want to explore the world beyond? What normal teenager doesn't want to explore a new neighborhood or city or country? And what person hasn't at one time or another dreamt of how it would feel to travel across the boundaries of time or space?

The urge to travel is universal. And this makes travel, as broadly defined, a very big business indeed. In the United States, for example, travel and tourism is estimated to account for approximately 5% of gross domestic product and to be the third largest retail industry after automobile dealers and food stores. Clearly, in getting from here to there and back again, we need lots of goods and services. In fact, including everything, the travel industry turns out to be the world's largest in terms of numbers of people employed and in terms of total direct and indirect revenues generated. Three hundred million people – one of every ten employees world-wide – and more than US$1.5 trillion out of a total world economic output of around US$40 trillion are probably good estimates for those numbers at the start of the twenty-first century.

With an industry so large, it is difficult to even know where to begin. There are texts relating to hotel or restaurant or casino management policies. There are tomes and stock brokerage house reports and consultants' papers providing forecasts for the various travel-related business segments. Statistics of all types abound.