The conventional view of international society has it 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 have been encouraged from the distinct constituency of world society. The book traces a series of historical case studies which issued in international affirmation of such principles: slave-trade abolition in 1815; the public conscience in 1899; social justice (but not racial equality) in 1919; human rights in 1945; and democracy as the only acceptable form of state in 1990. In each case, evidence is presented of world-society actors (transnational movements, advocacy networks, and INGOs) making the political running for a new principle, often in alliance with a leading state. At the same time, world society has mounted a normative case, and this can be seen as a degree of normative integration between international and world society. Collectively, the book contributes to the growing IR literature on the role of norms, and especially that written from a broadly English School or constructivist perspective.