Since the 2006 High-level Dialogue on International Migration and Development, organized by the United Nations General Assembly, and the creation of the Global Forum on Migration and Development, the issue of international migration has risen on the agenda of policymakers around the world. The increased demand for policy relevant migration information has exposed serious deficiencies in the availability of basic data on global migration levels, trends and characteristics. Many countries collect data on persons under 20 years of age, who were born outside the country of enumeration and who may or may not be a citizen of that country, usually as part of their population census or through administrative means, and at different intervals. While more information on migrant children and adolescents has become available in the recent past, harmonized estimates for all countries and areas in the world at regular intervals are currently not available. Answers to basic questions, such as “how many children and adolescents are participating in international migration?”, “what are the age profiles of those moving across borders?”, “do girls and boys have the same propensity to migrate?”, and “how does migration affects children and adolescents moving across borders and those who stay behind?” remain elusive.