Relatively few people enjoy the opportunity to travel to other countries. By far the most common form of travel is that by residents of a country within that country. International travel, although given high priority by segments of the populations of industrialized nations, is still a minority activity. As a very rough guide, we estimate that expenditure worldwide on domestic tourism may be worth up to ten times that amount on international tourism. Ironically, there are relatively few countries that collect domestic travel and tourism statistics, while much more information is available on international tourism. Why is this? First of all, international travel involves, by definition, the crossing of a frontier. It is therefore easier to observe and monitor. Domestic tourism involves movement internally and is therefore more difficult to research. Countries that only make use of registration forms at hotels miss out on all aspects of domestic tourism that involve staying in other accommodation establishments or with friends or relatives. A number of countries do not even try to measure domestic tourism due to its very nature. For example, in many developing countries, very little domestic movement involves staying in paid accommodation, and so it does not compete with demand from international visitors.