Why are some international agreements informal?

Informal agreements are the most common form of international cooperation and the least studied. Ranging from simple oral deals to detailed executive agreements, they permit states to conclude profitable bargains without the formality of treaties. They differ from treaties in more than just a procedural sense. Treaties are designed, by long-standing convention, to raise the credibility of promises by staking national reputation on their adherence. Informal agreements have a more ambiguous status and are useful for precisely that reason. They are chosen to avoid formal and visible national pledges, to avoid the political obstacles of ratification, to reach agreements quickly and quietly, and to provide flexibility for subsequent modification or even renunciation. They differ from formal agreements not because their substance is less important (the Cuban missile crisis was solved by informal agreement) but because the underlying promises are less visible and more equivocal. The prevalence of such informal devices thus reveals not only the possibilities of international cooperation but also the practical obstacles and the institutional limits to endogenous enforcement.