The present Innocenti Insight draws on research conducted in eight advanced industrialized countries: Australia, France, Germany, Italy, the Netherlands, Switzerland, the United Kingdom and the United States. These are countries that, together, include almost 40 per cent of all persons in the world who are not living in their countries of birth. The general profile of this significant share of the world’s immigrant population is relatively well understood, in part because of the growing political and policy interest in migration questions. The same, however, cannot be said about the segment of this population represented by children. Indeed, children’s situation and experience has been largely missing from the migration debate and from related efforts in data collection and analysis. The Innocenti Insight presents, for the first time, internationally comparable data addressing the number, share and family circumstances of immigrant children in these eight affluent nations. It contributes statistical evidence and enables a deeper understanding of the magnitude and diversity of national and social backgrounds, as well as living conditions and opportunities for migrant children in destination countries. And it provides a sound foundation to inform social policies that can address factors leading to deprivation and marginalization of immigrant children and to more effectively promote their social inclusion and harmonious development.