In the span of a few days in the spring of 1999, hundreds of thousands of ethnic Albanians fled their homes in Kosovo as Serbian forces drove them into neighboring countries. At the time, I was a new medical school graduate put in charge of triaging sick and injured refugees who showed up in a constant stream at an improvised medical aid station in the cold, muddy no-man’s-land between Kosovo and Macedonia. As I stood there, I could see thousands of men, women and children who had trudged across the border or arrived in trucks, cars, horse-drawn carts or the arms of fellow refugees. Their numbers taxed the ability of overstretched United Nations refugee officials to track them. Many families had been abruptly separated during the chaos of expulsion. Once inside the border in refugee camps, desperate mothers and fathers posted paper notes with names and descriptions of their missing children.