The term ‘contracting state’ describes a state which has consented to be bound by a treaty, even though it may not yet have entered into force (Article 2(1)(f)). A ‘party’ is a state which has consented to be bound by a treaty and for which the treaty is in force (Article 2(1)(g)). At that point – and only then – is the state bound by the treaty (Article 26), although certain procedural-type provisions will be operative even before. To consent to be bound is therefore the most significant, positive act which a state can take in relation to any treaty. This chapter explains the various means by which consent can be expressed. The next chapter deals with entry into force. However, as will be explained, although two quite distinct steps are necessary to become a party – express consent to be bound by the treaty and its entry into force – someimes they can take place at the same time.

Participation in a treaty

In Chapter 4 we saw which entities can be parties to treaties, but this does not mean that the main entity, a state, can be a party to any treaty. This should be clear in the case of bilateral treaties. But whether a state (or another subject of international law, such as an international organisation) can participate in a multilateral treaty depends entirely on the terms of the treaty.