The recurrent instability of the international monetary system is usually assessed in either purely economic or purely political terms. Economists explain the durability of a dominant International Reserve Currency (IRC) by referencing transaction costs and deep markets. International relations scholars explain the durability of an IRC by referencing power political factors like control over oil or military dominance. Instead, I make an imperfect analogy between international money and domestic money to understand why the usual factors are necessary but not sufficient for establishing an IRC. The imperfections in this analogy show that the incomplete legitimacy of the IRC and its issuing state create the inherent tendency towards international monetary disorder. Domestic money and credit systems are inherently unstable because banks tend to create too much “inside money” and thus trigger a credit crisis. Only the state, which issues “outside money,” can validate inside money in a crisis. But outside money is only legitimate over a political space in which actors have representation and a single actor is authoritative, and an economic space from which private actors cannot exit. The international political economy lacks both features, creating instability as capital flows across different economies.