Currently, the central questions in the philosophical debate surrounding the ethics of automated warfare are (1) Is the development and use of autonomous lethal robotic systems for military purposes consistent with (existing) international laws of war and received just war theory?; and (2) does the creation and use of such machines improve the moral caliber of modern warfare? However, both of these approaches have significant problems, and thus we need to start exploring alternative approaches. In this paper, I ask whether (...) autonomous robots ought to be programmed to be pacifists. The answer arrived at is “Yes”, if we decide to create autonomous robots, they ought to be pacifists. This is to say that robots ought not to be programmed to willingly and intentionally kill human beings, or, by extension, participate in or promote warfare, as something that predictably involves the killing of humans. Insofar as we are the ones that will be determining the content of the robot’s value system, then we ought to program robots to be pacifists, rather than ‘warists’. This is (in part) because we ought to be pacifists, and creating and programming machines to be “autonomous lethal robotic systems” directly violates this normative demand on us. There are no mitigating reasons to program lethal autonomous machines to contribute to or participate in warfare. Even if the use of autonomous lethal robotic systems could be consistent with received just war theory and the international laws of war, and even if their involvement could make warfare less inhumane in certain ways, these reasons do not compensate for the ubiquitous harms characteristic of modern warfare. In this paper, I provide four main reasons why autonomous robots ought to be pacifists, most of which do not depend on the truth of pacifism. The strong claim being argued for here is that automated warfare ought not to be pursued. The weaker claim being argued for here is that automated warfare ought not to be pursued, unless it is the most pacifist option available at the time, and other alternatives have been reasonably explored, and we are simultaneously promoting a (long term) pacifist agenda in (many) other ways. Thus, the more ambitious goal of this paper is to convince readers that automated warfare is something that we ought not to promote or pursue, while the more modest—and I suspect, more palatable—goal is to spark sustained critical discussion about the assumptions underlying the drive towards automated warfare, and to generate legitimate consideration of its pacifist alternatives,in theory, policy, and practice. (shrink)