When Beatles star John Lennon faced deportation from the U.S. in the 1970s, his lawyer, Leon Wildes, made a groundbreaking argument. He argued that Lennon should be granted “nonpriority” status pursuant to the prosecutorial discretion policy of the Immigration and Naturalization Service (INS)—a policy maintained by the INS’s successor, the Department of Homeland Security (DHS). In U.S. immigration law, the relevant federal agency exercises prosecutorial discretion favorably when it refrains from enforcing the full scope of the law against one or more persons. A prosecutorial discretion grant is important to an agency seeking to focus on the “truly dangerous,” conserve resources, and enforce immigration law with compassion. The Lennon case marked the first moment that the immigration agency’s prosecutorial discretion policy became public knowledge. Today, the concept of prosecutorial discretion is more widely known in light of the Obama administration’s Deferred Action for Childhood Arrivals (DACA) program, a record number of deportations, and the stalemate in Congress over immigration reform. This is the first book to comprehensively describe the history, theory, and application of prosecutorial discretion in immigration law, unveiling the powerful role it plays in protecting individuals from deportation and conserving government resources. Shoba Sivaprasad Wadhia draws on her experience as an immigration attorney, policy leader, and law professor to advocate for bolder standards of prosecutorial discretion, greater mechanisms for accountability when such standards are ignored, improved transparency about the cases involving prosecutorial discretion, and recognition of “deferred action” in the law as a formal benefit.