The European Trading Scheme (ETS) was developed to restrict greenhouse-gas emissions by setting mandatory caps on emissions each year. Initially, the ETS dealt only with power plants and other industrial businesses, but in 2008, the European Union (EU) (defendant) expanded the ETS to cover aviation by implementing the Aviation Directive (the Directive). The Directive covered flights arriving in or departing from any airport located within the EU, and provided standards for calculating emissions based on the entire length of the flight, including time flown over other countries and the high seas. After these total calculations, the airline would then be assessed for all emissions connected with the flight. The Directive was met with many objections, and in December 2009, three U.S. airlines and the Air Transport Association of America (plaintiffs) filed an action in the Queen’s Bench Division of the High Court of Justice of England and Wales. The airlines argued that the Directive had violated international-law limitations on jurisdiction through the Directive’s application to portions of flights occurring outside EU airspace. The action was referred to the European Court of Justice for consideration of the issue.