According to the Guide to Practice on Reservations to Treaties, adopted by the International Law Commission in 2011, updating and completing the definition with elements contained in other international conventions on the law of treaties,1 a reservation is “a unilateral statement, however phrased or named, made by a State or an international organization when signing, ratifying, formally confirming, accepting, approving or acceding to a treaty or by a State when making a notification of succession to a treaty, whereby the State or organization purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that State or to that international organization”.2
The conditions for the validity of reservations and their legal effects are set out in the Vienna Convention on the Law of Treaties,3 and in more detail, in the Guide to Practice.4 In general, the effect of an established reservation is to exclude the application of certain provisions of the treaty or of the treaty itself in respect of certain measures, industries or situations.5 A measure falling within the scope of a reservation is not governed by the treaty and cannot be assessed against the standards set out in the treaty.6
The ILC Guide to Practice does not discuss reservations to bilateral treaties.7 Although the definition does not exclude reservations made to bilateral treaties, a “reservation” to a bilateral treaty is only a proposal to renegotiate or to amend the treaty in question. If such a reservation is accepted by the other State in question, it becomes an amendment to the treaty.8 Therefore, there is no notable practice in respect of reservations to bilateral investment treaties or in the relevant decisions of arbitral tribunals.
Some multilateral investment treaties authorize specific reservations,9 others exclude reservations,10 and others remain silent on the question of reservations.11 In the last case, the customary international law principles concerning reservations to treaties, set out in the Vienna Convention and by the International Court of Justice,12 apply. Some tribunals have considered that the possibility provided for in multilateral investment instruments to opt out of certain obligations or of compulsory dispute resolution constitutes a reservation and need to be interpreted accordingly.13 Other tribunals were more reluctant to qualify this as a reservation in the sense of the 1969 Vienna Convention.14
A reservation is to be interpreted in accordance with the rules and principles of treaty interpretation,15 in good faith, taking into account the intention of the reserving State as expressed in the text of the reservation, as well as the object and purpose of the treaty and the circumstances in which the reservation was formulated.16 There is no general rule according to which a reservation is to be interpreted restrictively,17 although some tribunals have expressed the view that “exceptions” in a treaty are to be interpreted restrictively.18
Reservations need to be distinguished from interpretative declarations that do not produce the same legal effect and are not submitted to the same conditions. The decisive criterion is the legal effect that a unilateral statement would have on the treaty.19 The label or the name of the declaration provides only an indication of the purported effect but is not in itself decisive.20 If a declaration purports to modify the treaty, it is a reservation.21 If it purports to clarify the interpretation of the treaty, it is an interpretative declaration.22
Aust, A., Reservations, in Modern Treaty Law and Practice, 3rd ed., 2013, pp. 114–144.
Horn, F., Reservations and Interpretative Declarations to Multilateral Treaties, 1988, p. 514.
Pellet, A., The ILC Guide to Practice on Reservations to Treaties. A General Presentation by the Special Rapporteur, New York University School of Law – Jean Monnet Working Paper Series 15/12; European Journal of International Law, 2013‑4, pp. 1061‑1097.
Ruda, J. M., Reservations to treaties, Collected Courses of the Hague Academy of International Law, 1975-III, pp. 95–218.
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