Article 21 Vienna Convention on the Law of Treaties

Legal effects of reservations and of objections to reservations

1. A reservation established with regard to another party in accordance with articles 19, 20 and 23:
   (a) modifies for the reserving State in its relations with that other party the provisions of the treaty to
   which the reservation relates to the extent of the reservation; and
   (b) modifies those provisions to the same extent for that other party in its relations with the reserving
   State.
2. The reservation does not modify the provisions of the treaty for the other parties to the treaty
   inter se.
3. When a State objecting to a reservation has not opposed the entry into force of the treaty
   between itself and the reserving State, the provisions to which the reservation relates do not apply as
   between the two States to the extent of the reservation.

See also: Article 20 Vienna Convention on the Law of Treaties