It is said that nothing is constant except change. For industry trying to keep up with its environmental obligations, perhaps the more appropriate saying would be that nothing is constant except regulatory uncertainty. Under President Barack Obama, the U.S. Environmental Protection Agency (EPA) has pursued wide-sweeping regulatory initiatives under virtually every major environmental statute. These include the Agency's groundbreaking efforts to monitor and regulate mobile and stationary sources of greenhouse gases under the Clean Air Act. Complicating the regulatory landscape, the courts have overturned many of the George W. Bush EPA's rulemaking initiatives, sending the Agency back to the drawing board on a host of significant and broad-reaching rulemakings. As a result, industry faces perhaps the most uncertain environmental regulatory landscape in 20 years.