Editors' Summary: When Congress amended the Clean Air Act in 1990, it instituted a new approach to the regulation of hazardous air pollutants (HAPs). Although EPA had great discretion in adopting HAP emission standards prior to 1990, the Agency promulgated standards for only seven substances in two decades. The 1990 amendments changed this by requiring EPA to establish emission standards for over 100 HAPs enumerated in amended Clean Air Act § 112. Moreover, the amended Act mandates EPA to require new and existing sources to install maximum achievable control technology (MACT) and subject certain facilities to additional control if their residual emissions, after installation of MACT controls, still pose an unacceptable risk to exposed individuals. The authors examine this new approach to regulating HAPs by first analyzing HAP regulation under § 112 prior to enactment of the 1990 amendments. They then analyze amended § 112 and review the steps that EPA has taken to promulgate new HAP regulations. They explore some of the problems with preamendment § 112 that have been raised in Clean Air Act litigation and examine the ways in which Congress addressed these problems in the 1990 amendments. Finally, they conclude that despite Congress' revisions to § 112 and EPA's efforts to implement them, the new program may prove to be no more effective than the old one.