he requirement of legitimate authority—according to which ‘the right of initiating war in a state lies with the sovereign’—was originally introduced in the writings of Augustine, Aquinas, and Pufendorf. This chapter offers a detailed account of the Requirement as it should be understood and an articulation of the moral conviction that underlies it. The chapter then defends the Requirement by addressing the main objection to it: wars are just in virtue of their intrinsic features; it does not matter who fights them. In response to this objection, this chapter shows that Joseph Raz’s ‘normal justification thesis’ supports conferring authority to veto wars on two (usually overlapping) collectives: those on whose behalf the war is fought and those who will bear its costs. The chapter further advances a proceduralist justification of the Requirement arguing that violating it compromises the ideal of fair political participation.