The mitigation of air transport system environmental impacts has received significant and increasing attention over the last few decades. Today it is recognized as one of the fundamental pillars of the air transport value system alongside safety, efficiency and capacity, sustainment, and economic viability. The complexity of this issue is also generally accepted. Solutions can take on a variety of forms (e.g. vehicle technologies, operations and ATM technologies, economic and regulatory measures), multiple stakeholders are involved (manufacturers, airlines, airports, ATM, etc.), and difficult tradeoffs often arise between environmental improvements and other dimensions of the air transport system. This issue of the Journal Aerospace Operations presents a collection of high-quality papers that examine air transport environmental impacts from a variety of perspectives, collectively spanning acrossenvironmental impact mitigation solutions, environmental metrics, stakeholders, and modeling approaches.