Since Barack Obama was sworn in as President in 2009, the Environmental Protection Agency (EPA) has proposed and promulgated numerous regulations implementing the pollution control statutes enacted by Congress. Critics have reacted strongly. Many, both within Congress and outside of it, have accused the agency of reaching beyond the authority given it by Congress and ignoring or underestimating the costs and economic impacts of proposed and promulgated rules. The House has conducted vigorous oversight of the agency in the 112th Congress, and has approved several bills that would overturn specific regulations or limit the agency's authority. Particular attention is being paid to the Clean Air Act, under which EPA has moved forward with the first federal controls on emissions of greenhouse gases and also addressed emissions of conventional pollutants from a number of industries. Environmental groups disagree that the agency has overreached, and EPA states that critics' focus on the cost of controls obscures the benefits of new regulations, which, it estimates, far exceed the costs; and it maintains that pollution control is an important source of economic activity, exports, and American jobs. Further, the agency and its supporters say that EPA is carrying out the mandates detailed by Congress in the federal environmental statutes. This report provides background information on recent EPA regulatory activity to help address these issues. It examines 40 major or controversial regulatory actions taken by or under development at EPA since January 2009, providing details on the regulatory action itself, presenting an estimated timeline for completion of the rule (including identification of related court or statutory deadlines), and, in general, providing EPA's estimates of costs and benefits, where available. The report includes tables that show which rules have been finalized and which remain under development. The report also discusses factors that affect the timeframe in which regulations take effect, including statutory and judicial deadlines, public comment periods, judicial review, and permitting procedures, the net results of which are that existing facilities are likely to have several years before being required to comply with most of the regulatory actions under discussion. Unable to account for such factors, which will vary from case to case, timelines that show dates for proposal and promulgation of EPA standards effectively underestimate the complexities of the regulatory process and overstate the near-term impact of many of the regulatory actions.