Most wars today are civil wars, but we have little understanding of the conditions under which rebel groups might comply with the laws of war. I ask three questions in this essay: What do the laws of war require of rebels, or armed nonstate actors (ANSAs)? To what extent are rebels aware of the laws of war? Under what conditions do rebel groups comply with international humanitarian law? I argue that the war aims of rebel groups are key to understanding their relationship with the laws of war. In particular, secessionist rebel groups–those that seek a new, independent state–are especially likely to comply with the laws of war as a means to signal their capacity and willingness to be good citizens of the international community to which they seek admission.