In this issue brief, Mariano-Florentino Cuéllar examines a little-noticed way in which the burgeoning focus on homeland security since the attacks of 9-11 has affected domestic regulatory policy. He argues that the government reorganization that took place when the Department of Homeland Security (DHS) was created, which included converting the U.S. Coast Guard into a bureau within the vast new DHS bureaucracy, is taking a toll on protection of the environment. According to the paper, the Coast Guard has significant responsibilities for protecting the environment; indeed, it has over twice as many employees as the entire Environmental Protection Agency, and its employees work on missions of comparable environmental importance. The Coast Guard is charged with limiting risks from dangerous oil spills, guarding against toxic chemical leaks from ship engines, regulating the cruise ship industry, and protecting against over-fishing and the elimination of marine endangered species. But as part of DHS, Cuéllar writes, the Coast Guard's environmental mandate is being eclipsed by other priorities, and its already-scarce resources strained by new demands. The result, he concludes, is a significant decline in the hours it devotes to environmental protection activities, the size of the budget it allocates to them, and the regulatory actions it is taking on critical environmental matters. Professor Cuéllar analyzes these changes and recommends vigorous Congressional oversight and action to put the Coast Guard's environmental protection mission back on course.