This article attempts to fill a gap in the literature about civilian control by presenting the concept of control from within the military and investigating its determinants. Control from within is the intentional action taken by soldiers tasked with missions with which they disagree in an attempt to affect how the military implements politically based directives. The forms of control from within include restraining the aggressiveness of other soldiers, whistle-blowing, selective and gray refusal to deploy, foot-dragging, collective bargaining about deployments, and documentation and testimonies. By drawing on the cases of the US and Israeli militaries, I argue that the interplay of two variables determines the choice made by soldiers tasked with missions with which they disagree: the level of presence of potentially subversive soldiers belonging to the same social group; and the group’s social status within and outside the military. These variables are strongly affected by the type of manpower system. Under conscription, both variables exert a powerful effect, encouraging the exercising of control from within. In contrast, a volunteer system reduces the influence of the two variables, so control from within is more restricted, and dissatisfied soldiers may favor other forms of action with a limited impact on military policies.