More and more people are flying. In 2018 alone, worldwide passenger air traffic will increase by 6.7 percent compared to the previous year. And it continues to grow. This means that the negative effects are also growing. With this brochure, the German Environment Agency (UBA) is therefore addressing an important and at the same time very complex issue. How much air traffic is actually necessary? At what cost to humans, the climate and the environment will it be affordable in the future? How can we achieve a change in transport that not only affects aircraft and airports, but also changes in the economy and consumer behavior?