Editors' Summary: In the first of two Articles, Professor Craig N. Oren examines the recent "blockbuster" opinion in American Trucking Ass'n v. United States Environmental Protection Agency, in which a panel of the D.C. Circuit Court of Appeals remanded EPA's air quality standards for ozone and particulate matter. The author begins with a discussion of the statutory and regulatory framework and describes the court's holding. From there, the Article moves to a detailed explanation of the reasons why the oft-articulated concerns about possible revival of the delegation doctrine are overstated. Professor Oren asserts that American Trucking should, instead, properly be viewed as a finding that the EPA was arbitrary and capricious in setting the standards because the Agency's decisions were insufficiently explained. The Article suggests that while American Trucking signals the need for reexamination of the criteria for establishing ambient air quality standards, a number of obstacles, perhaps insurmountable, stand in the way of meaningful reform. Expressly incorporating cost considerations would, the Article notes, complicate regulatory analyses. Moreover, overt consideration of cost would arguably be inconsistent with the statutory goal of public health protection. Nor is the alternative approach suggested by Judge Williams in American Trucking, based on an Oregon Medicaid program, likely to succeed in the CAA context. Professor Oren argues that the agency responses that occurred subsequent to the Lockout/Tagout and Vinyl Chloride decisions are, likewise, of doubtful assistance. Perhaps, the Article contends, the time has come for courts to provide the EPA increased deference in the setting of air quality standards. Although American Trucking likely does not mark the resurrection of the delegation doctrine, Professor Oren concludes that the decision will undoubtedly significantly complicate the process of developing ambient air quality standards.