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 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.  Nevertheless, the Vienna Agreement allows the CEN or ISO to carry out standardization activities on the same subject if deemed necessary. The Joint ISO-CEN Coordinating Group of the Technical Boards plays an important strategic role in monitoring the implementation of the Viennese Agreement and consulting with the CEN`s Senior Technical Committee and the ISO Technical Technical Committee on all matters related to the Viennese Agreement, including the need for revisions. In September 2001, a revised version (version 3.3) of the “Vienna” agreement was published, which reduced the agreement itself to the essential principles of cooperation between ISO and the NEC. Overall, the current version of international standardization gives priority and gives more importance to ISO leadership than previous versions. For example, ISO standards can only be revised under ISO`s direction, regardless of their origin. In 1996, CENELEC and the CIS signed the Dresden Agreement to create the framework for an intensive consensus process between the development of European and international standards in the electricity sector.
In order to avoid duplication between de-derisation at international and European level, to the benefit of contributors and users of standards, as well as to improve the effectiveness of standardisation at European and international level, CEN and CENELEC have signed agreements with their respective international partners, the International Standards Organisation (ISO) and the International Electrotechnical Commission (IEC) on the rules of cooperation. The Viennese Convention, signed in 1991 between the CEN and ISO, recognises the primacy of international standards and aims to simultaneously recognise standards at international and European level by improving information exchange and mutual representation at meetings. Either the NEEc or ISO take the lead in the development of a new standard and the related documents are submitted by both parties for simultaneous approval.