Editors' Summary: The Environmental Protection Agency (EPA) has long been embroiled in controversy over its regulation of hazardous air pollutants under §112 of the Clean Air Act. The Act requires rapid, stringent regulation of pollutants EPA lists as hazardous, but leaves it to EPA to decide what to list. In the 16 years since §112's enactment, EPA has listed only a handful of pollutants and been slow to regulate those it has listed. The Act encourages caution in listing pollutants, since it can be read to require protection of public health at all costs and regulation must follow listing. Environmentalists have fought for expansive listing of likely carcinogens and other dangerous chemicals in exchange for accepting best available technology standards instead of zero risk standards. They have been unsuccessful in administrative proceedings and Congress alike. Now they are in court, attacking a new EPA approach that expands the coverage of §112, but regulates only significant risks that can be controlled with technological ease and little economic disruption. The litigation could chart the future of §112 and is a major test of the risk assessment policies adopted with great fanfare by former EPA Administrator William Ruckelshaus.