Dr. Kelly Greenhill is an associate professor at Tufts University and a research fellow in the Belfer Center's International Security Program at Harvard University. She studies the security of migration change. Her work focuses on new security challenges, including forced migrations, and how these may be used as a political weapon or a tool for diplomacy. Her recent book, Weapons of Mass Migration: Forced Displacement, Coercion, and Foreign Policy, won the 2011 International Studies Association's Best Book of the Year award. Greenhill also was a co-author and co-editor (with Peter Andreas) of Sex, Drugs and Body Counts: The Politics of Numbers in Global Crime and Conflict. She spoke with the Journal about her work and how she sees forced migrations playing out on today's world stage.