The United Nations Convention on Contracts for the International Sale of Goods (CISG) has reached the level of acceptance that it can be recognized as the face of international sales law. Over a century ago, the late Roscoe Pound drew attention to the dichotomy between the law as written and the law as experienced in practice. The law of the CISG “on the books” is the law of the United States. With the growth of international trade, one might expect its importance to grow in the realm of law “in action.” This article explores the CISG in action in U.S. courts during its almost four decades of being the law on the books in the United States. To this end, the authors built an original dataset based on their Westlaw search of all decisions mentioning the CISG across all U.S. federal and state courts from 1988 (when the CISG entered into force) through 2019. The dataset provides unprecedented insights into: (1) how parties raise the issue of the applicability of the CISG, (2) how courts have ruled on the Convention's applicability, and (3) the provisions of the Convention that appear most frequently in these disputes. This article empirically assesses, through logistic regressions, which factors are statistically significant for predicting if a court will apply (or decline to apply) the Convention to a disputed transaction. Finally, the article highlights many ways in which the law in action may not be as robust or comprehensive as it appears on the books.