Abstract: Criminal informants occupy a central role in the US criminal system. Police rely heavily on criminal suspects to obtain information and get warrants, whereas prosecutors often use defendants as information sources in exchange for dropped charges or shorter sentences. This is particularly true in drug cases, which comprise approximately 30 percent of state and federal dockets but are not limited to that arena. The informant deal is widely used in every class of offense, from white-collar crime to child pornography to murder. Although many types of people give information to the government, criminal informants constitute a uniquely important and problematic class of witness because they are offenders who trade information in exchange for leniency for their own offenses. Unlike whistle-blowers or citizens who call 911, criminal informants (sometimes referred to as snitches) provide information in hope of escaping punishment for their own crimes, which has contributed to their well-documented unreliability, among other issues. At the same time, because the government tolerates or even forgives informants’ criminal activities, the informant deal has become a problematic crime-management policy in its own right as well as an independent source of crime in some instances. Criminal informant policies have wide-ranging legal, cultural, and racial implications. For example, because drug enforcement—and thus informant use—is concentrated in poor, minority communities, those neighborhoods have been overexposed to the phenomenon. Consequences include increased crime and violence, unreliable evidence used in warrants and prosecutions, and community distrust of police. The so-called stop snitching phenomenon expressed in rap music and other aspects of popular culture is in part a result of this dynamic. Criminal informants have also been important features in the evolution of the Federal Bureau of Investigation (FBI), the white-collar enforcement strategies of the US Department of Justice, and most recently the war on terror. Finally, the law of informant use is changing; legislatures and governmental commissions in New York, California, Texas, Illinois, and Florida, among others, have considered or passed legal reform.