This is a story of hope in the face of widespread consternation over the global climate crisis. For many people concerned about global warming, the 2018 vote by UK parliamentarians to proceed with the plans for a third runway at Heathrow Airport was a devastating blow. Aviation was predicted to make up some 25% of the UK's carbon emissions by 2050 and so the decision seemed to fly in the face of the UK's commitment to be a climate leader. Can the UK expand Heathrow airport, bringing in 700 extra planes a day, and still stay within ambitious carbon budgets? One legal case sought to answer this question. Campaigning lawyers argued that plans for a third runway at one of the world's busiest airports would jeopardise the UK's ability to meet its commitments under the 2015 Paris Agreement on climate change. This book traces the dramatic story of how the case was prepared - and why international aviation has for so long avoided meaningful limits on its expansion.