The agreement applies only to written contracts between states. The first part of the document defines the terms and scope of the agreement. The second part sets out the rules governing the conclusion and adoption of contracts, including the agreement of contracting parties and the formulation of reservations, i.e. the refusal to be bound by one or more specific provisions of a contract, while they accept the rest. The third part deals with the application and interpretation of contracts and the fourth part examines the possibilities of amending or amending contracts. These parts essentially codify existing customary law. The most important part of the agreement, Part V, sets out the reasons and rules governing the non-publication, termination or suspension of contracts and contains a provision that gives the International Court of Justice jurisdiction over disputes arising from the application of these provisions. The last parties discuss the impact on treaties on changes in government within a state, changes in consular relations between states and the outbreak of hostilities between states, as well as rules on custodians, registration and ratification. However, agreements between states and international organizations or between international organizations themselves are governed by the 1986 Vienna Convention on treaty law between states and international organizations or between international organizations when it enters into force. Moreover, in treaties between states and international organizations, the provisions of the Convention continue to apply between states.  The convention does not apply to unwritten agreements.  The Convention applies only to contracts concluded after its development and to contracts between states and therefore does not regulate agreements between states and international organizations or between international organisations themselves, but if one of their rules is binding on these organizations, they will remain so. The VCLT applies to interstate contracts within an intergovernmental organization.  The Vienna Convention on Treaty Law (VCLT) is an international agreement governing treaties between states.  The contract, known as the “contract,” contains detailed rules, procedures and guidelines for the definition, development, modification, interpretation and general operation of contracts.  The VCLT is considered to be the codification of customary international law and state contract practice.  Vienna Convention on Treaty Law, an international agreement on treaties between states, drawn up by the UN Commission on International Law and adopted on 23 May 1969 and entered into force on 27 January 1980. To learn more about the Joint Protocol on the implementation of the Vienna Convention and the Paris Convention, visit our website on multilateral agreements. The Convention codifies several foundations of contemporary international law. It defines a treaty as “an international agreement that is written and governed by international law between states” and asserts that “every state has the capacity to conclude treaties.” Article 1 limits the application of the convention to written contracts between states, with the exception of treaties between states and international organizations or international organizations themselves. Article 26 defines pacta sunt servanda, article 53 proclaims the mandatory standard, and Article 62 proclaims a fundamental change in circumstances. Thirty-five UN member states had to ratify the treaty before it could enter into force.