This article addresses the "monitoring paradox" that public enforcers may face in attempting to oversee private gatekeepers. Governments frequently enlist private parties to serve as gatekeepers because they possess special skills or advantages that allow them to detect and prevent wrongdoing by their clients or suppliers in a cost-effective way. However, the same skills or advantages that enable gatekeepers to monitor wrongdoing often provide them with the means and the incentives to subvert their duties and to evade public oversight. This article provides an innovative solution to this challenge by showing how governments may overcome their inability to oversee gatekeepers by providing other private actors, such as victims, qui tam litigants, informants, or even the targeted wrongdoers themselves, with incentives to serve as monitors of gatekeeper compliance. This article will apply this framework for private monitoring of gatekeepers to the chronic failure of efforts to enlist employers as gatekeepers for immigration enforcement. This private monitoring approach coupled with a set of complementary reforms and safeguards offers a cost-effective way to provide employers with incentives to comply with their duties to confirm the immigration status of employees and thus to reduce economic incentives for illegal immigration.