The GCMD holds more than 25,000 Earth science data set and service descriptions, which cover subject areas within the Earth and environmental sciences. The project mission is to assist researchers, policy makers, and the public in the discovery of and access to data, related services, and ancillary information (which includes descriptions of instruments and platforms) relevant to global change and Earth science research. Within this mission, the directory also offers online authoring tools to providers of data and services, facilitating the capability to make their products available to the Earth science community. In addition, citation information to properly credit data set contributions is offered, along with direct links to data and services. As an integral part of the project, keyword vocabularies have been developed and are constantly being refined and expanded. These vocabularies are also used in other applications within the broader scientific community. Users may perform searches through the Directory's website using controlled keywords, free-text searches, map/date searches or any combination of these. Users may also search or refine a search by data center, location, instrument, platform, project, or temporal/spatial resolution. Today, the GCMD is one of the largest public metadata inventories in the world. The GCMD's primary responsibility is to maintain a complete catalog of all NASA's Earth science data sets and services. The project also serves as one of NASA's contributions to the international Committee on Earth Observation Satellites (CEOS), through which it is known as the CEOS International Directory Network (IDN).