The legitimacy of the military is frequently overlooked in standard accounts of jus ad bellum. Accordingly, this paper considers how the military should be organized. It proposes a normative conception of legitimacy -the 'Moderate Instrumentalist Approach' -that outlines the qualities that a military should possess. It then assesses the three leading ways of organizing the military according to this approach: the use of private military and security companies (PMSCs), a conscripted force and the all-volunteer force (AVF). The paper argues that the AVF, despite some notable problems, is the most legitimate way of organizing the military.