 to an agency's interpretation of an ambiguous law. So, for instance, when Congress wants to regulate some pollutant, it doesn't say, here's the formula you use to decide exactly how to regulate this at power plants. It tells the EPA, figure out how much of this is harmful, limit it in accordance. This decision today says, you know what? Federal courts don't have to defer to what the scientists at the EPA say. Federal courts can make their own decisions about precisely what the law requires and impose those views on agencies.