This report establishes that international humanitarian law regulating air-to-air attacks (offensive as well as defensive) is located in several different legal sources, whose applicability is not always clear. The first Additional Protocol to the Geneva Conventions is applicable to air-to-air attacks which may affect the civilian population, individual civilians or civilian objects on land. Otherwise, air-to-air attacks are mainly governed by customary international law, as the Missile and Air Warfare Manual and the ICRC's study of customary international humanitarian law intended to specify. The report describes which legal source forms the basis for the applicability of the fundamental principles of distinction, proportionality and precautions in air-to-air attacks, and describes how these principles regulate such attacks. Further, the current working characterization of lethal autonomous weapons systems is analysed in relation to fighter aircraft. Finally, the report identifies questions for further research on how existing and emerging international humanitarian law should be understood in relation to autonomous combat functions in fighter aircrafts. The report concludes by identifying a need for Swedish research on existing and emerging international humanitarian law applicable to air-to-air warfare, based on Swedish international legal obligations, interpretations and positions.