As a part of the 1990 amendments to the Clean Air Act, Congress required the EPA to conduct “periodic, scientifically reviewed studies to assess the benefits and the costs of the Clean Air Act.” In other words, Congress wanted to know whether the Act “was worth it.” The initial report in what is now a series was released in October 1997. The evaluation provided a detailed retrospective analysis of costs and benefits from the years 1970 to 1990 and showed that the overwhelming benefits obtained from compliance with the Act far outweighed the costs of implementation.