Commitment and Diffusion: How and Why National Constitutions Incorporate International Law

This paper considers why it is that drafters of national constitutions incorporate international law, a phenomenon that is of growing importance. It argues that designers do so when they need to make credible commitments, and that international law has some unique features that render it attractive as a commitment device. The paper then considers an alternative hypothesis, namely that countries adopt such provisions as part of a process of diffusion, following other country's choices. The paper develops an empirical test of these hypotheses, and finds support for both, suggesting that commitment and diffusion operate in a complementary fashion.