Although many features of bilateral investment treaties (bit s) are consistent from one agreement to the next, a closer look reveals that the treaties exhibit considerable variation in terms of their enforcement provisions, which legal scholars have singled out as the central component of the treaties. An original data set is compiled that captures three important treaty-design differences: whether the parties consent in advance to international arbitration, whether they allow treaty obligations to be enforced before an institutionalized arbitration body, and how many arbitration options are specified for enforcement. Drawing upon several relevant literatures on international institutions, three potentially generalizable explanations for this important treaty variation are articulated and tested. The strongest support is found for the theoretical perspective that emphasizes the bargaining power and preferences of capital-exporting states, which use the treaties to codify strong, credible investor protections in all their treaties. Empirical tests consistently reveal that treaties contain strong enforcement provisions—in which the parties preconsent to multiple, often institutionalized arbitration options—when the capital-exporting treaty partner has considerable bargaining power and contains domestic actors that prefer such arrangements, such as large multinational corporations or right-wing governments. In contrast, there is no evidence to support the popular hands-tying explanation, which predicts that investment-seeking states with the most severe credibility problems, due to poor reputations or weak domestic institutions, will bind themselves to treaties with stronger investment protections. Likewise, little support is found for explanations derived from the project on the rational design of international institutions, which discounts the identities and preferences of the treaty partners and instead emphasizes the structural conditions they jointly face. In sum, this foundational study of differences across investment treaties suggests that the design of treaties is driven by powerful states, which include elements in the treaties that serve their interests, regardless of the treaty partner or the current strategic setting.