What role do expertise and specialization play in regulatory regimes that deploy private litigation as an enforcement tool? This question is of enormous practical importance to the optimal design of law enforcement across a range of regulatory areas, from securities and antitrust to environmental protection and civil rights. Yet it has generated surprisingly little rigorous empirical analysis. This Article begins to fill that gap by offering the first large-scale empirical study of a growing and increasingly controversial litigation regime in which debate about the role of specialized private enforcers has taken center stage: qui tam lawsuits brought under the False Claims Act (“FCA”). Using an original data set of more than 4,000 qui tam suits filed between 1986 and 2011, this Article tests, and mostly rejects, a pair of what might be called “supply-side” critiques of the regime: first, that qui tam litigation is inefficiently dominated by a growing cadre of repeat, “professional” plaintiffs; and second, that qui tam’s explosive growth and seeming excesses can be attributed to an increasingly specialized qui tam plaintiffs’ bar. The findings demonstrate that, contrary to a chorus of critics, specialized relator-side firms appear to play a positive role in the system, enjoying higher litigation success rates and surfacing larger frauds than less experienced firms. Similarly, while repeat relators win less often than one-shotters, they offset lower win rates by obtaining substantially larger recoveries when they succeed. These findings offer a much-needed empirical baseline for evaluating legal and policy debate around the FCA as well as leading proposals for its reform. More broadly, exploring the role of expertise and specialization in a specific, microinstitutional context such as qui tam is a first step to developing a thicker and more systematic account of the possibilities and limits of private enforcement of public law.