This chapter analyses the background to the signing of the 2015 Paris Agreement on Climate Change by almost every nation on Earth. It traces the creation of the UK’s Climate Change Act 2008, which has been called one of the world’s leading legislative attempts to reduce greenhouse gas emissions, and the 2008 Planning Act which formed the backbone of the Heathrow legal challenge. This story shows the complexity of the approach taken by campaigning lawyers. The chapter also introduces the matter of why aviation’s international nature means that the industry has escaped regulation of its CO2 emissions at the domestic level. It also explores the poorly understood ‘non-CO2 emissions’ from aviation.