The conventional view of international society is that it is interested only in co-existence and order amongst states. This creates a puzzle. When the historical record is examined, we discover that international society has repeatedly signed up to normative principles that go well beyond this purpose. When it has done so, it has built new normative constraints into international legitimacy, and this is most conspicuously so when it has espoused broadly humanitarian principles. This suggests that the norms adopted by international society might be encouraged from the distinct constituency of world society.