The Supreme Court’s ruling in Massachusetts v. EPA made clear that greenhouse gases fall within the realm of air pollutants the Clean Air Act was designed to regulate. The Court’s decision sparked a chain reaction forcing the EPA to regulate greenhouse gases under different provisions of the Act. The EPA’s decision to regulate drew fierce criticism, especially from industries that would be forced to reduce emissions. Opponents argue that greenhouse gases are not traditional pollutants and therefore the drafters of the Clean Air Act did not intend them to be regulated. Furthermore, they argue that the EPA over-stepped its authority in “tailoring” a new rule to incorporate greenhouse gases more appropriately into the Act’s framework. This Note defends the EPA’s decision to regulate greenhouse gases, as well as its Tailoring Rule. In light of the Clean Air Act’s explicit language and legislative intent, the EPA was not only legally justified in implements its decision, but it had no other choice.