Over the past few decades, the aviation sector has been constantly growing, and has consequently been attributing to higher amounts of environmentally unfriendly carbon emissions. Without a doubt, there was no more time to waste to counteract this trend. Amongst the potential options, extending the European cap and trade scheme (EU ETS) to aviation activities and creating a Single European Sky (SES) is not just interesting from an environmental and economic perspective, but also from a legal point of view. With regard to the EU ETS, particularly the ECJ’s ATA-judgment is analysed in greater depth, and is therefore at the centre of attention. This judgment is unquestionably a landmark decision with very controversial global effects. In fact, many scholars, stakeholders, etc have expressed their discontent with respect to the Court’s arguments. The focus of the second central subject (SES) is on the defragmentation of the European airspace. The creation of so-called Functional Airspace Blocks, which can probably be regarded as the key element of the SES, is capable of considerably reducing aviation’s CO2 emissions. Some interesting legal issues (sovereignty and subsidiarity concerns) also arose in this connection. This book shall help to explain the need to act in the context of aviation’s CO2 emissions, and to comprehend the European way of thinking.