As the number of migrants, refugees, and asylum seekers have grown worldwide, intense debate has emerged about how long and how well they integrate into host countries. Although integration is a complex process, realized differently by different groups at different times, most prior studies capture, at best, disparate parts of the process. Overcoming this limitation is a tall task because it requires data and research that capture how integration is both dynamic and contextual and requires focusing on conceptual issues, emphasizing how integration varies across spatial scales, and including perspectives of the process through the eyes of both scholars and practitioners. This special issue of The ANNALS of the American Academy of Political and Social Science presents research that uniquely enhances our understanding about the breadth of the integration process in the United States, Canada, and European countries. Edited by Katharine Donato and Elizabeth Ferris, the volume is a product of the Global Refugee and Migration Project, a two-year collaboration between the Institute for the Study of International Migration and the Berkley Center.