This article proposes and evaluates four hypotheses about US pollution and environmental policy over the last half century. First, air and water pollution have declined substantially, although greenhouse gas emissions have not. Second, environmental policy explains a large share of these trends....

This article proposes and evaluates four hypotheses about US pollution and environmental policy over the last half century. First, air and water pollution have declined substantially, although greenhouse gas emissions have not. Second, environmental policy explains a large share of these trends....