This extraordinarily well-written, well-researched article by Michael Livermore and Ricky Revesz makes a significant contribution to the literature and public policy debates by challenging conventional wisdom—namely, that health-based NAAQS are more stringent (and hence more protective) than those that would be set were we to consider the costs of achieving those standards. The authors carefully, and to my mind convincingly, debunk the idea that health-based standards are necessarily more protective than those that might be based on cost/benefit analysis  or other economic considerations, providing facts rather than unsubstantiated rhetoric. This information is new and it is dramatic. While I believe there is much here that will fuel constructive consideration of a critical issue, I have two concerns: aspects of their characterization of how health-based standards are set; and their reading/analysis of the relevant Supreme Court precedent.