This article posits that the creation and development of international regulatory regimes has so far required a choice between rulemaking and adjudication. Regulators that wish to make policy broadly and prospectively have done so informally and through rules. More elaborate and powerful regulatory regimes, however, have tended to feature the creation of an adjudicator. This choice of policymaking form has important, but often overlooked, procedural consequences. Choice of form affects the effectiveness, flexibility, accountability, and transparency of an international regulatory regime. The article examines three characteristic ways that international regulators make rules. For adjudication, it introduces three tribunals that exemplify that process. It uses the distinction between rulemaking and adjudication to organize these disparate international institutions and concludes with recommendations that would help to increase the formality of the new breed of international rulemakers, and conversely increase the flexibility of the new set of international tribunals.