Given that their main function is to forge durable commitments, it is notable that many international treaties change over time through the practice of renegotiation. While some agreements have remained intact after their initial conclusion, others are amended, updated, or replaced. Why are some international agreements renegotiated while others remain stable? This paper offers a systematic analysis of treaty renegotiation by presenting theoretical propositions and testing them in the context of bilateral investment treaties (BITs). We argue that states renegotiate when they learn new information about the legal and political consequences of their treaty commitments, and that such learning is most likely to take place when states are involved in investor-state dispute settlement cases. Employing an original data set on renegotiated BITs, we find robust empirical support for the learning argument. We conclude by discussing implications for the study of institutional change and the evolving investment regime.