Reservations to Treaties

In one line

A reservation is a unilateral statement by which a State excludes or modifies the effect of certain provisions in their application to itself, and it is permitted unless the treaty forbids it or it is incompatible with the treaty's object and purpose.

The definition

Article 2(1)(d). A reservation means a unilateral statement, however phrased or named, made by a State when signing, ratifying, accepting, approving or acceding to a treaty, whereby it purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that State.

Four points hide in that sentence.

However phrased or named. A State cannot escape the law of reservations by calling its statement a declaration, an understanding or an interpretative statement. What matters is whether it purports to exclude or modify legal effect.

At the moment of expressing consent. A reservation is made when signing, ratifying, accepting, approving or acceding, and not later. A State that has become a party without reservation cannot add one afterwards, except with the agreement of the other parties.

Certain provisions. A reservation is directed at identified provisions. A statement rejecting the whole treaty is not a reservation; it is a refusal to be a party.

In their application to that State. A reservation changes the treaty for the reserving State and for those dealing with it. It cannot change the treaty for anybody else, which article 21(2) makes explicit.

A reservation is not the same as an interpretative declaration. A genuine interpretative declaration says what the State understands a provision to mean, without excluding or modifying its effect. If in substance it excludes or modifies effect, it is a reservation whatever its label, because article 2(1)(d) says however phrased or named.

The old rule and the case that ended it

Before 1951 the rule was unanimity: a reservation was effective only if every other contracting party accepted it, and a single objection kept the reserving State out of the treaty altogether. That rule suited treaties among few States. It did not suit the general multilateral conventions of the United Nations era, where hundreds of States were wanted as parties.

Reservations to the Genocide Convention, ICJ Reports 1951, p. 15

The question. By a resolution of 16 November 1950 the General Assembly asked the Court three questions about the Convention on the Prevention and Punishment of the Crime of Genocide, which contained no article on reservations. Could a State that ratified or acceded subject to a reservation objected to by some parties but not others be regarded as a party while maintaining the reservation? If so, what was the effect of the reservation as between the reserving State and the objecting parties, and as between it and the accepting parties? What was the legal effect of an objection made by a signatory that had not yet ratified, or by a State entitled to sign or accede that had not done so?