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International law is central to the interpretation of both of the Brexit-related treaties. The TCA explicitly requires the parties and any dispute settlement body to interpret it according to the rules of interpretation of public international law, notably the 1969 Vienna Convention on the Law of Treaties (VCLT). The WA, and thus the Protocol, by specifying that any of its provisions concerning Union law or concepts must be interpreted in accordance with EU law (including the case law of the CJEU), implies that its many provisions not concerning EU law will need to be interpreted by the default rules of treaty interpretation, namely those of the VCLT. This chapter provides a brief overview of those rules and some of their implications for these two instruments. It focuses on Articles 31 and 32 of the VCLT, which concern the interpretation of treaties.


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