Yesterday, Justice Scalia, writing for a majority of the United States Supreme Court, invalidated EPA's greenhouse-gas (GHG) regulations to the extent they require stationary sources to obtain a Prevention of Significant Deterioration (PSD) and/or Title V major source permit based solely on the source's GHG emissions. The Court, however, also validated EPA's extension of "best available control technology" (BACT) requirements to GHG emissions at sources already subject to PSD requirements based on criteria pollutant emissions (so-called "PSD-anyway" sources). Thus, while EPA's authority to require BACT controls for GHGs at so-called PSD-anyway sources was upheld, the broad scope of authority claimed by EPA was significantly reduced. The case, Utility Air Regulatory Group v. EPA ("UARG"), No. 12-1146, is a significant development in EPA's efforts at regulating GHGs in the absence of Congressional action and, as discussed below, raises a number of important issues and questions.