Treaty reservations and declarations explained

Reservation or declaration

Article 2 of the Vienna Convention defines a reservation as a unilateral statement, whatever its wording or name, made when a state signs, ratifies, accepts, approves or accedes to a treaty ¹. The name used does not decide the matter. What counts is whether the statement purports to exclude or modify a provision ¹.

The UN Treaty Handbook, revised in 2013, describes an interpretative declaration as a state's statement of its understanding of a matter or of a particular provision ². It says an interpretative declaration does not have a legal effect similar to that of a reservation ². Optional and mandatory declarations are different again. The Handbook says they are legally binding on the declarants ².

When a reservation is not allowed

Article 19 of the Vienna Convention lists cases in which a reservation cannot be formulated, starting with a reservation the treaty prohibits ¹. The Paris Agreement says in Article 27 that no reservations may be made to it ³. The Treaty Handbook gives the Kyoto Protocol as another treaty that expressly prohibits reservations ².

A reservation made at signature of a treaty subject to ratification must be formally confirmed when the state expresses its consent to be bound ¹.

Objections and the twelve-month clock

Under Article 20 of the Vienna Convention, a reservation is considered accepted by a state that has raised no objection by the end of twelve months after being notified, or by the date it consented to be bound, whichever is later ¹.

The Treaty Handbook describes late reservations, made after a state has already become a party. It records that the UN Legal Counsel advised that the time limit for objecting to such a late reservation would be 12 months from the date of the depositary notification ².

Withdrawing a reservation

Article 22 says a reservation may be withdrawn at any time, except where the treaty provides otherwise, and the consent of states that accepted it is not required ¹. The withdrawal becomes operative for another state only when that state receives notice of it ¹. The Treaty Handbook says the withdrawal must be in writing and signed by the Head of State, Head of Government or Minister for Foreign Affairs or a person with full powers ².

Examples in the UN Treaty Collection

The status page for the Rome Statute of the International Criminal Court records declarations made under Article 87 on the channel and language for requests from the Court. Hungary asked for requests through the diplomatic channel in English, and Mali asked for requests in French ⁴.

The Paris Agreement status page records that by a communication received on 2 July 2024, Denmark withdrew its declaration on the territorial exclusion of Greenland ⁵. Each such statement and its withdrawal sits in the depositary record next to the state's ratification.