Population mobility and migration (see Definitions) have become permanent facets of a rapidly globalising world. Propelled by modern transport technology and communication systems, people from all regions of the world are moving at a much faster pace. Globalisation has changed not only the scope, but also the patterns of migratory movements, from traditional, more permanent movement in one direction, to a repeated and bi-directional movement of people that is referred to as circulatory migration or repeated return.1
Population dynamics, with international migration as an increasingly important component, is envisaged to affect development in both developing and developed countries.2 Migration affects population growth, age and sex structures. In emigration countries, it depletes cohorts, mostly at young adult ages, and it increases the youth bulge in immigration countries.3 Along with unemployment and poverty, population growth is higher among developing and least developed countries. In contrast, developed countries, which have low and declining fertility, are experiencing shrinking working-age populations and rapid population ageing. This is the case in Japan4 where the working age (15-64) population is projected to fall from 85 million in 2005 to 72 million in 2025. Thus, Japan is debating whether to open itself to frontdoor immigrants to stabilise the population and labour force, admit side-door guest workers who would be expected to leave after several years, or keep migration doors mostly closed and persuade Japanese workers to work longer and more productively. Research shows that international migration can play a role in limiting population decline and reductions of the working-age population and population ageing, especially in countries with low fertility, although it cannot reverse these trends.