The National Optical Astronomy Observatory (NOAO) was the United States national observatory for ground-based nighttime ultraviolet-optical-infrared (OUVIR) astronomy. The National Science Foundation (NSF) funded NOAO to provide forefront astronomical research facilities for US astronomers. Professional astronomers from any country in the world could apply to use the telescopes operated by NOAO under the NSF's "open skies" policy.
NOAO was operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the NSF. Its headquarters in Tucson, Arizona, were co-located with the headquarters of the National Solar Observatory. The budget for NOAO during the 2017 fiscal year was nearly $23 million.