The Application of Estoppel in International Law and Experiences for Vietnam

In international relation, estoppel is a principle whereby a state is not able to say or act against what it said or did before. The theory of estoppel was originated in the past from the English law system, which was later incorporated into international law. Its main purpose is to prevent a State from benefiting from its inconsistent attitudes, and thus, causing damage to another State. Therefore, estoppel must meet the main conditions. First, the expression of the said State leads to the assumption of the estoppel must be clear and non-ambiguous. Second, this expression must be expressed voluntarily, unconditionally and must be well authorized. Third, there must be a goodwill trust from another State into the expression of a State giving that expression, resulting in damage to the State with this trust or to the benefit of the expressive side. The paper examines the principle of estoppel in international law and the practice of applying this principle in cases tried at the International Court of Justice. On that basis, the paper discusses explaining the factors that constitute an estoppel situation for Vietnam in order to reject the China’s wrong interpretation of the 1958 Diplomatic Note of the late Prime Minister Pham Van Dong.