The air quality and biological diversity of the western United States pose special problems for future research. For those who desire generality this diversity provides a challenge to find general patterns that cover the West. For those, such as regulators, who need information on particular sites, the West provides an overwhelming number of potential special cases. Thus the West also exemplifies the problem of the relationship between two kinds of scientific activity: the search for generality and the determination of particulars. Here the author proposes that future studies should include many more comparative analyses to address this problem. In this view the diversity of the West becomes a major scientific resource.