Emissions of nitrogen oxides (NOx ) contribute to formation of particulate matter and ozone, and also to acidification of the environment. The electricity sector is responsible for about 20% of NOx emissions in the United States, and the sector has been the target of both prescriptive (command-and-control) and flexible (cap-and-trade) approaches to regulation. We summarize the major NOx control policies affecting this sector, and provide some perspectives as to their effectiveness. While both prescriptive and flexible approaches continue to play an important role, significant new proposals have wholly embraced a cap-and-trade approach.