an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation (article 2(1)(a) of VCLT)

a document emanating from the competent authority of a State designating a person or persons to represent the State for negotiating, adopting, or authenticating the text of a treaty, for expressing the consent of the State to be bound by a treaty, or for accomplishing any other act with respect to a treaty.

(a) Heads of State, Heads of Government and Ministers for Foreign Affairs, for the purpose of

performing all acts relating to the conclusion of a treaty;

(b) heads of diplomatic missions, for the purpose of adopting the text of a treaty between the

accrediting State and the State to which they are accredited;

(c) representatives accredited by States to an international conference or to an international

organization or one of its organs, for the purpose of adopting the text of a treaty in that conference, organization, or organ.  

(article 7(2) of VCLT)

According to article 11 of VCLT, “the consent of a State to be bound by a treaty may be expressed by signature, exchange of instruments constituting a treaty, ratification, acceptance, approval or accession, or by any other means if so agreed.”

The consent of a state to be bound to a treaty may be invalidated owing to an error, fraud, corruption of the state representative, coercion of a representative of a state, and coercion of a state by the threat or use of force.

Per article 26 of VCLT, the state bound by a treaty must perform the terms of the treaty in good faith