If internal and international migrants comprised a nation, it would be the third most populous¹ country in the world, just after China and India. Thus, there can be little doubt that population mobility² is among the leading policy issues of the 21st century. However, policies to protect migrants and global health have so far been hampered³（阻碍，限制） by inadequate⁴ policy attention and poor international coordination⁵. This is the conclusion of a new article in PLoS Medicine arguing that current policy-making on migration⁶ and health has been conducted within sector⁷ silos（粮仓） , which frequently have different goals. Yet, population mobility is wholly compatible with health-promoting strategies for migrants if decision-makers coordinate⁸ across borders and policy sectors⁹, say the authors, who are also serving as guest editors of a new series in PLoS Medicine on migration & health that launches this week. In the first article in the series, Cathy Zimmerman, Ligia Kiss, and Mazeda Hossain from the London School of Hygiene¹⁰ & Tropical Medicine (LSHTM), United Kingdom, lay out a new framework that describes migration as a multi-staged process involving numerous health risks and intervention¹¹ opportunities. This migration-health framework benefits international and local policy-makers by highlighting various points for intervention and options for coordination between nations. Five subsequent articles in the series discuss in-depth the health impacts and policy needs associated with the five phases of this migratory¹² process: pre-departure, travel, destination, interception¹³, and return.

The second article in the series, by Brian Gushulak and Douglas MacPherson from Migration Health Consultants¹⁴ in Canada, is also published in this week's PLoS Medicine and discusses the specific health risks and policy needs associated with pre-departure. Subsequent articles in the series, to be published weekly until 21 June 2011, will discuss the remaining stages of the migration process.