This book is concerned with the government of 'illegal' immigration since the passage of the U.S. Immigration Act of 1965, exploring how certain mentalities and intellectual machineries have rendered illegal immigrants as targets of government. It examines how various authorities have created knowledge about and constructed 'illegal' immigration as an ethical problem. It analyzes the tactics that have been deployed to govern immigration, particularly at the US-Mexico border. Using an ethnographic approach, it draws on primary source materials - including government publications, archival documents, newspapers, and popular magazines. It studies measures (e.g. Operation Gatekeeper and Operation Hold-the-Line) for reforming the conduct of 'illegal' immigrants in order to forestall illicit border crossings. It frames the study of immigration within Foucauldian theories of governmentality. It highlights the role of numbers and statistics in constructing the 'illegal' immigrant.