A central challenge in the modern regulatory state is rationalizing and coordinating multiple, overlapping, and interdependent public and private enforcement mechanisms. To that end, recent years have seen mounting calls to vest administrative agencies with litigation “gatekeeper” authority across a range of regulatory areas, from environmental protection and civil rights to antitrust and securities. Agencies, it is said, can use their expertise and synoptic perspective to weigh costs and benefits and determine whether private rights of action should lie at all. Alternatively, agencies might be given the power to evaluate lawsuits on a case-by-case basis, blocking bad cases, aiding good ones, and otherwise husbanding available private enforcement capacity in ways that conserve scarce public resources for other uses. Yet despite the proliferation of such calls, there exists strikingly little theory or evidence on how agency gatekeeper authority either should or would work in practice. This Article aims to fill that gap by offering a systematic account of this often-invoked but under-theorized role for agencies. Drawing on theories of agency behavior and empirical analysis of the gatekeeper regimes currently in existence, this Article sketches the case for and against vesting agencies with litigation gatekeeper authority across a range of regulatory contexts and elaborates some functional design principles that policymakers can use to weigh competing models or determine whether agency gatekeeping makes sense at all. There are other pay-offs as well. Anatomizing agency gatekeeping allows us to reimagine the agency role in some of our most consequential regulatory regimes, among them a system of job discrimination regulation that seems especially ripe for revision following the Supreme Court’s decision in Wal-Mart v. Dukes. More broadly, this Article makes a novel contribution to the otherwise oceanic literature on “litigation reforms” and reorients scholarly debate around optimal regulatory design and the contours and purposes of the administrative state itself by exploring the increasingly blurred boundary between administration and litigation.