Abstract: This article examines a counterintuitive phenomenon: cases where claims of police expertise do not bolster but undercut police authority in court. Assertions of unique insight, training, and experience have long provided officers with a reliable claim to deference, deflecting a range of challenges to police misconduct. Yet in a variety of disputes, from coerced confessions to entrapment to excessive force, policemen’s comparative expertise emerges in the opposite posture, stoking judicial discomfort with enforcement tactics and driving adverse holdings against the state. The gap between these strategies, I argue, reflects a tension between two fundamentally distinct conceptions of expertise: what this article identifies as seeing expertise as a professional virtue or a professional technology. The virtuous view imagines expertise as a de facto institutional good, commanding authority because it presumptively improves enforcement outcomes or, simply enough, because it is valuable in itself. The technological view, by contrast, imagines it simply as an asset that facilitates the performance of investigative tasks, expanding police power in the field and thereby—like the more familiar technologies of policing, from surveillance devices to location trackers—reconfiguring what courts see as the proper balance of power between the individual and the state. Far from invariably deflecting criticism, by this view, the significance of police expertise rests on its interplay with the specific values animating the courts’ procedural doctrines in any case: what the police are expert at and how those skills intersect with the goals of a given genre of review. The courts’ dual approaches to police expertise illuminate debates about deference and competency in and beyond the criminal law. For one thing, they expose the moralistic assumptions undergirding our shared intuitions about expertise as a source of institutional authority, urging greater skepticism of a range of legal doctrines grounded on judicial self-abnegation to ostensibly more expert actors. At the same time, they complicate the conventional link between expertise and authority itself, revealing the ambiguous relationship between competency and legitimacy in a system administered by multiple, often-conflicting agents of the law. Not least, they invite us to confront our commitment to certain government tasks, like so many apparently entrusted to the police, that ironically inspire less controversy the less masterfully they are performed. Building on these insights, this article contends that courts should take a technological view of expertise in all their encounters with law enforcement, a shift that will yield more rigorous scrutiny of a broad range of police behavior. In a legal system populated by an increasingly professionalized police force, we must do away with the assumption that more expert policing is, invariably, more lawful policing, and recognize how that development raises new issues for—and imposes novel obligations on—judges committed to the protection of individual rights.