<p>Models of problem and responsible gambling have long emphasized personal responsibility, informed choice, and player agency as central to preventing gambling-related harm. Yet gambling harm occurs within broader commercial and regulatory systems, raising questions about how responsibility is distributed across players, operators, and regulators. In a study of 297 American adults, we examined responsibility attributions for online gambling-related harm and whether gambling history, problem gambling severity, and online gambling activity shape these attributions. Participants attributed the greatest responsibility to players, but also substantial responsibility to operators and regulators, suggesting that gambling-related harm is perceived as a shared responsibility rather than solely a player-level issue. Participants who gambled and those who did not gamble showed similar mean responsibility attributions, although responsibility judgments were more zero-sum among those who gambled: greater player responsibility was associated with lower operator and regulator responsibility. Among those who gambled, higher problem gambling severity predicted greater responsibility attributed to operators and regulators, whereas greater online gambling activity predicted greater responsibility attributed to operators. Neither predictor was associated with lower player responsibility. Finally, responsibility attributed to operators and regulators, but not players, predicted stronger support for stricter online gambling regulation. These findings suggest that greater gambling involvement and harm may heighten recognition of system-level responsibility without diminishing perceived player agency. They also point to a shared-responsibility model in which player agency remains important, but operator and regulator accountability are central to how the public understands and responds to online gambling harm.</p>