We provide the first empirical assessment of commenter influence during the rule development stage of administrative rulemaking. We argue that public com-menters play a critical agenda-setting role during rule development. To test this proposition, we analyze data from 36 Department of Transportation rules and almost 500 comments. Each of these rules began with an Advance Notice of Proposed Rulemaking—a procedure that allows us to track the formal participation of interested parties during rule development. Our analyses are supplemented by face-to-face interviews with agency officials. We find a strong agenda-setting role for early commenters—both in terms of affecting the content of future regulations and in thwarting unwanted regulations. We conclude that “early-bird” com-menters are well positioned to frame public policy debates as rules move through the regulatory process. © 2009 by the Association for Public Policy Analysis and Management.