Artikel 40

1. Unless the treaty otherwise provides, the amendment of multilateral treaties shall be governed by the following paragraphs.
2. Any proposal to amend a multilateral treaty as between all the parties must be notified to all the contracting States and all the contracting organizations, each one of which shall have the right to take part in:
(a) the decision as to the action to be taken in regard to such proposal;
(b) the negotiation and conclusion of any agreement for the amendment of the treaty.
3. Every State or international organization entitled to become a party to the treaty shall also be entitled to become a party to the treaty as amended.
4. The amending agreement does not bind any State or international organization already a party to the treaty which does not become a party to the amending agreement; article 30, paragraph 4(b), applies in relation to such State or organization.
5. Any State or international organization which becomes a party to the treaty after the entry into force of the amending agreement shall, failing an expression of a different intention by that State or that organization:
(a) be considered as a party to the treaty as amended; and
(b) be considered as a party to the unamended treaty in relation to any party to the treaty not bound by the amending agreement.