A critical case was argued before the U.S. Supreme Court late February that has major implications for the electric utility industry and future efforts by the Environmental Protection Agency (EPA) to curb greenhouse gas emissions. The case is called Utility Air Regulatory Group v. EPA and it will determine whether or not the EPA acted legally when it granted itself the authority to regulate greenhouse gas (GHG) emissions from stationary emitters such as power plants.

When most people think of laws today, they think of legislation passed by Congress. Yet, the primary source of law that governs society today developed from common law. In a common law legal system, laws are developed by judges through decisions of courts and similar tribunals, rather than by legislation. A majority of the rules of contract law, tort law, property law, and criminal law evolved from common law, while legislation served to simply codify decisions or fill in areas not covered by case law.

Without question, the U.S. legal system, from the structure and operations of the judicial branch to the governing laws of the nation, was founded in the common law legal tradition. Common law, for those unfamiliar with the concept, is law that develops organically over time and is based on the accepted customs and shared values of a society. More specific to its history, common law was developed in England as it emerged from the Middle Ages, where the legal systems of the disparate regions were united by royal decrees and the decisions of judges based not on the wisdom of the given monarch or judge, but on previous decisions made in other legal cases.