Multilateral environmental agreements (MEAs) are one of the key instruments of international environmental governance and international environmental law. They are separate treaties to which States, regional economic integration organizations and, in some instances, and international organizations have become a Party. They intend to promote international cooperation on a specific set of environmental issues, such as the protection of the ozone layer and biodiversity and sustainable management of hazardous chemicals and waste. The United Nations Secretary-General usually serves as the depositary for each treaty.