II Interpretation and Intertemporal Application of Investment Treaties

This chapter examines the interpretation and intertemporal application of investment treaties. In international investment law, the interpretation of treaties takes place by tribunals whose composition varies from case to case. This makes it more difficult to develop a consistent case law than in a permanent judicial institution. Most tribunals, when interpreting treaties, start by invoking Article 31 of the Vienna Convention on the Law of Treaties (VCLT). Tribunals have recognized the validity of the rules on treaty interpretation in the VCLT as part of customary international law. This means that these rules are of general application also in respect of treaties concluded before the VCLT’s entry into force in 1980 and independently of whether all parties to a treaty have ratified the VCLT. At times, tribunals also refer to the supplementary means of interpretation contained in Article 32 of the VCLT. Meanwhile, some treaties provide for a consultation mechanism concerning their interpretation or application.