The U.S. Environmental Protection Agency estimates that federal air quality policies impose annual costs in excess of $80 billion ($2010) with the primary goal of improving human health. An area of research, sometimes termed “accountability,” aims to quantify these benefits, and sometimes costs, to understand the true impact of regulatory actions. We review recent studies on accountability and contrast their research designs. Key challenges to accountability research are discussed and future directions suggested. Most accountability studies investigated short-term impacts at a local scale, taking advantage of rapid changes in air quality due to policy interventions, such as for the Olympic Games. While useful, this research framework is not applicable to more extensive regulatory actions that deal with long-range transport, large spatial scales, and longer timeframes. A growing number of accountability studies investigate these issues, although the development of additional methods is needed. Challenges inherent to accountability research are vast and include the choice of baseline pollution and health response levels, transboundary pollution from outside the study area, limitations in exposure approaches (e.g., air quality modeling), and extrapolation of epidemiological studies from other populations or geographic areas. Findings from accountability research can help decision-makers design the most effective air quality policies, but in many cases such studies are hindered by large uncertainties. Given the challenges in accountability research, extensive sensitivity analyses and use of multiple methods would provide more compelling evidence than the use of any single approach.