The Environmental Protection Agency (EPA) took another dramatic step toward comprehensive regulation of greenhouse gases (GHGs) last week when it committed to issue sector-wide New Source Performance Standards (NSPS) to control GHG emissions from fossil-fuel based power plants and petroleum refineries. Responsible for almost 40% of GHGs emitted in the United States, application of the new NSPS to these two industries is expected to have a significant impact on GHG emissions in this country. While Congressional efforts over the past few years to control GHGs through comprehensive cap and trade programs generated much public discourse and awareness, federal, state, regional, and local governments and regulatory agencies have been working behind the scenes to limit GHG emissions, largely through regulation. To the surprise of many, because of these regulatory efforts, the death of federal cap and trade in Congress has not meant the end of GHG regulation in the United States. Instead, it is the beginning of what promises to become a comprehensive, mandatory regulatory scheme, involving all levels of government, that within the next three to five years will control GHGs in all sectors of the economy. Instead of the flexible, market-based controls contemplated by federal cap and trade, however, businesses will face more stringent, and likely more costly, compulsory mandates requiring reductions in GHG emissions.