Why do states express support for norms that go against their underlying beliefs? Scholars of policy diffusion have identified four social mechanisms -- coercion, competition, emulation, and learning -- that can lead to the spread of a common practice, a norm, in the international system. I build a formal model of the four mechanisms and apply them to actual cases of norm diffusion. The formal models are anchored by three variables that capture fundamental aspects of international society: hierarchy, neighborhood, and identity. The four different diffusion mechanisms operate on these variables, creating distinct over-time trajectories. Three important dynamic patterns are compared across different model specifications: the shape of the adoption S-curve, the power distribution among expressers and non-expressers, and the degree of regional clustering. I find that the four mechanisms produce unique signatures under many conditions, but that changes to some parameters such as initial number of expressers can obscure the identification of the diffusion mechanism. In the first empirical chapter, I apply the framework to the diffusion of quotas for women's representation. I find that quotas are adopted by weak states, and that the likely source of inspiration for quota adoption are other weak states in the same neighborhood. The empirical pattern in terms of hierarchy, neighborhood, and identity point to competition as the mechanism that drove quota diffusion. Because competition is associated with norm internalization, this finding suggests that the world is really becoming more gender equal. In the second empirical chapter, I change substantive focus to the diffusion of human rights norms. Adoption of human rights treaties seems to be associated with worse human rights behavior, but why do states that ratify human rights treaties so often fail to uphold their obligations?. I find that the Convention Against Torture (CAT) treaty is adopted first by strong states in Europe, then to weaker states in a regionally-contingent pattern. This empirical pattern is most consistent with the emulation mechanism. This implies that the anti-torture norm is not associated with internalization, and solves the previously puzzling ratification-compliance paradox.