Abstract : Fully Autonomous Weapon Systems (AWS), or “killer robots”, once activated, can select and attack targets without further human intervention. Autonomous Weapons Systems have raised two related ethical concerns: a) it may be wrong to give a machine control over potentially lethal activities, b) the use of AWS may create undesired gaps in responsibility attributions for military (wrong) actions. Governmental and non-governmental actors have insisted on the ethical principle of “meaningful human control” over Autonomous Weapon Systems to preserve human moral responsibility; but they have recognized the lack of a philosophical theory to give this principle a precise content. This paper aims at laying the foundation of a philosophical theory of meaningful human control over autonomous systems based on insights from the “compatibilist” literature on free will and moral responsibility, in particular the concept of “guidance control” as elaborated by Fischer & Ravizza (1998). The paper aims at giving a fresh contribution to computer and robot ethics, by systematically introducing into it an analysis of control based on the philosophical literature on free will and moral responsibility; it also aims at giving fresh contribution to the compatibilist theory of moral responsibility, by elaborating a new philosophical framework for understanding one particular kind of human control, i.e. meaningful human control over autonomous robotic systems.