The conclusion of an international treaty consists of two stages:
a) the first stage is a harmonizing of wills of States or of other subjects of international law with regard to rules of conduct, i.e. concerning the text of the treaty. In concluding bilateral treaties this includes negotiations between parties and arriving at accord on the text of the treaty. In concluding multilateral treaties this stage consists in the drafting and adoption of the text of the treaty by the corresponding international conference or organ of an international organization. At multilateral conferences the text of the treaty is adopted by a two-thirds majority of the participants unless other provisions are made.
b) the second stage concerns a harmonizing of the wills of States concerning their recognition of the norms of the treaty as binding and consists of individual actions by States that may differ depending on the relevant terms of specific treaties (signing, ratification, etc).
Although the Vienna Convention itself does not provide a definition, “adoption” is generally defined as the formal act signifying that the form and content of the treaty have been agreed upon. Adoption signifies that the negotiations have been completed, disputed points have been resolved, and the wording of the final document agreed
The signing of the treaty may, by itself, signify the state's definitive consent to be bound when: the treaty states that the signature is a signal of the state's definitive consent; it is otherwise established by the contracting parties; or intent that the signature establishes definitive consent is indicated from the "full powers" document or otherwise expressed during the negotiations.
Historically, ratification was the process of verifying the authority given the representatives who had negotiated and signed a treaty, but the modern understanding in many states is that ratification is a check on the treaty-making powers of the executive branch by passing the treaty through the parliamentary/legislative branch of government. Ratification provides an additional opportunity to carefully consider the rights and obligations of a treaty before consenting to be bound by its terms. The law of treaties, as reflected in the Vienna Convention, does not require ratification for a state to be bound by a treaty, and many informal international agreements bind parties on the basis of a signature alone.
Accession is the process by which a state which was not a signatory of the treaty may nevertheless become a party to the treaty and be bound to its terms. Parties to a treaty are not given different treatment according to the manner in which they became parties.
Article 14 of the Vienna Convention refers to "acceptance" as "an expression of consent to be bound either without a signature or after a non-binding prior signature." Acceptance is not so much an actual method of consent as it is a term seen in treaty provisions, the meaning of which varies according to the context.
The term "approval" was introduced into international law to correspond to the internal procedures of states which call for the "approval" of treaties.
Entry into force is the actual implementation of the treaty's terms and in the Vienna Convention is governed by article 24. Entry into force often occurs when specific requirements laid out in the treaty have been met.