The effects of international institutions on state behavior make up a key research agenda in international-relations scholarship. Because states self-select into treaties, we cannot infer that these commitments have causal effects unless we address this selection effect. I explain the significant limitations of the methods used thus far to overcome this problem and argue that a more effective approach must take into account states’ treaty preferences. I describe a novel combination of ideal-point estimation and propensity-score matching that can estimate the probabilities of treaty commitment and use them to test hypotheses. I use this procedure to test the effects of three key international human-rights treaties. My results provide significant new findings regarding the effects of these important agreements. I show that the Convention on the Elimination of All Forms of Discrimination against Women has significantly improved respect for women's rights, but that the Convention against Torture and the International Covenant on Civil and Political Rights have not had significant effects on human rights.