The New Zealand Supreme Court in Bathurst Resources Limited v L & M Coal Holdings Limited (Bathurst Resources Limited v L&M Coal Holdings Limited [2021] NZSC 85) recently explored the issue of evidence of subsequent conduct in the interpretation of contracts. Generally, the role of subsequent conduct is limited. In 2018, the United Nations International Law Commission (ILC) examined in detail the use of subsequent agreements and practice in the interpretation of international treaties under art 31(3)(a) & (b) and art 32 of the Vienna Convention on the Law of Treaties (VCLT) (70th Session – Subsequent agreements and subsequent practice in relation to the interpretation of treaties [2018] (ILC Subsequent Practice)). Despite the contrast between contracts and treaties, the ILC’s work can be valuable to the Supreme Court. This article explores how.