"The U.S. Environmental Protection Agency (EPA) has the simple yet profound charge "to protect human health and the environment." EPA scientists apply their expertise to protect the public from air and water pollution, clean up hazardous waste, and study emerging threats such as global warming. Because each year brings new and potentially toxic chemicals into our homes and workplaces, because air pollution still threatens our public health, and because environmental challenges are becoming more complex and global, a strong and capable EPA is more important than ever. Yet challenges from industry lobbyists and some political leaders to the agency's decisions have too often led to the suppression and distortion of the scientific findings underlying those decisions -- to the detriment of both science and the health of our nation. While every regulatory agency must balance scientific findings with other considerations, policy makers need access to the highest-quality scientific information to make fully informed decisions. Concern over this problem led the Union of Concerned Scientists (UCS) to investigate political interference in science at the EPA. The investigation combines dozens of interviews with current and former EPA staff, analysis of government documents, more than 1,600 responses to a survey sent to current EPA scientists, and written comments from EPA scientists. The results of these investigations show an agency under siege from political pressures. On numerous issues -- ranging from mercury pollution to groundwater contamination to climate change -- political appointees have edited scientific documents, manipulated scientific assessments, and generally sought to undermine the science behind dozens of EPA regulations. These findings highlight the need for strong reforms to protect EPA scientists, make agency decision making more transparent, and reduce politicization of the regulatory process."