Mae Ngai traces the invention of the 'illegal alien' in American law and society, explaining how illegal migration became central to U.S. immigration policy. The story begins with the national-origin quotas of the 1920s, which created new categories of people who could be in America without permission. Ngai, a historian at Columbia University, offers close readings of the legal architecture of restriction: the statutes, court decisions, administrative enforcement practices, and differential treatment of European versus non-European migrants. She shows how immigration restriction remapped America both by creating new racial categories and by emphasizing the nation's land borders and their patrol as never before. The book examines how these legal changes affected particular communities, from Filipinos to Mexicans to Chinese Americans. Ngai demonstrates that 'illegal' status is not a natural category but a constructed one, produced by specific policy choices with specific consequences. Her analysis reveals how enforcement created a permanent population of people without rights, and how this shaped ideas about citizenship, race, and state authority throughout the twentieth century. This rigorously researched work is essential for understanding contemporary immigration debates and the historical forces that created them.