Under the Vienna Convention on the Law of Treaties (VCLT), article 11, the means of expressing consent may be carried out by

signature; instrument exchange;

Ratification: Although it's not always the case, in theory, treaties take effect upon signature. Ratification is an extra requirement for most treaties. Ratification is "the international act whereby a State establishes on an international plane its consent to be bound by a treaty," according to Article 1(b) of the VCLTThere is no set process because this is a matter for the national laws of the individual states. After the treaty is signed, each state has a "second chance" to either reaffirm its intent to be bound by it or change its domestic laws to comply with the treaty's requirements. It should be noted that ratification binds a state internationally and that a treaty (which requires ratification) does not bind the state until it has been ratified; however, the state is required to refrain from taking any action that would undermine the treaty's goals (article 18 of the VCLT).

Acceptance, approval, or accession: these are the methods by which a state that did not sign the original treaty can join it. It deposits a notice of accession to accomplish this. Either the parties to the original treaty must consent to the "new" state joining the treaty, or the original treaty must permit accession.

or any other method that the parties decide upon.