MIGRATION IS referred to as “any residential movement which occurs between administrative units over a given period of time,” according to geographers Paul White and Robert Woods (1980). Other scholars have defined migration as the change in the center of gravity of an individual’s mobility pattern. The destinations of the mobility flows need not, themselves, change as a result of the change in their center of gravity. For example, in the local intraurban move, the destinations of journey-to-work, recreation, and shopping may remain the same, while in an interurban move, they are likely to change. The perception of spatial differentiation of opportunities—the idea that different geographical locations offer different levels of potential well-being to various sections of human population— explains why migration occurs. It is these perceived differences between places that are important rather than any simple “push and pull” mechanism. Hence, migration occurs because migrants believe that they will be more satisfied in their needs and desires in the place that they move to rather than the place from which they come. An importance must be placed on the word believe. Migration occurs as a result of decisions made by individuals in the light of what they perceive the objective world to be like: it does not matter if the migrant holds an erroneous view—it is that erroneous view that is acted upon rather than the objective real-world situation. Thus, there may be cases where migration occurs despite the lack of an objective reason for it, and other cases where an objective appraisal of the world, were it possible, might suggest that migration should occur where it is, in fact, absent. In recent times, international migration is at record levels and is unlikely to slow down in the near future. The number of long-term international migrants (that is, those residing in foreign counties for more than 1 year), according to the United Nations Population Division, in 1965 was only 75 million, but that number rose to 84 million by 1975 and 105 million by 1985. There were an estimated 120 million migrants in 1990, the last year for which the detailed statistics are available. In the 1990s, migration growth continued with the same pace; hence, in 2000, an estimated 150 million people resided outside their county of birth or nationality. Even with the numbers of international migrants large and growing, it is important to keep in mind that less than 3 percent of the world’s population has been living outside their home countries for a year or longer. International migrants come from all parts of the world and they go to all parts of the world. In fact, only a few countries are unaffected by international migration. Many countries are sources of international flows, while others are net receivers, and still others are transit countries through which migrants pass to reach to receiving countries. Such countries as Mexico experience all 3 capacities, as source, receiving, and transit countries. The noteworthy fact about migration is that it tends to be within regions; migrants often remain within the same continent. More than half of international migrants traditionally have moved from 1 developing country to another. In recent years, however, migration from poorer to richer countries has increased significantly. While the traditional immigration countries—the United States, Canada, and Australia— continue to see large-scale movements as a result of labor recruitment that began in the 1960s and 1970s, , the oil-rich Persian Gulf states, and the “economic tigers” of East and Southeast Asia are now also major destinations for international migrants.