The introduction sets forth the concept of prosecutorial discretion in immigration law. It also explains how the book is organized and the author’s reasons for writing it. “Prosecutorial discretion” refers to a decision by a government employee or attorney or the acting immigration agency (as opposed to a judge) to abstain from enforcing the immigration laws against a person or group of persons. Public interest over prosecutorial discretion peaked in June 2012 when President Barack Obama announced a program called Deferred Action for Childhood Arrivals (DACA). Critics labeled the administration’s memoranda on prosecutorial discretion and DACA as excessive and politically motivated. Whether or not these policies were widely publicized for political reasons, understanding prosecutorial discretion and the important role it plays in U.S. immigration law is essential.