| Type: | Office |
| Agency Name: | Nautical Almanac Office |
| Jurisdiction: | Government of the United Kingdom |
| Headquarters: | Taunton, Somerset |
| Formed: | 1832–current |
| Parent Agency: | United Kingdom Hydrographic Office |
His Majesty's Nautical Almanac Office (HMNAO), now part of the United Kingdom Hydrographic Office, was established in 1832 on the site of the Royal Observatory, Greenwich (ROG), where The Nautical Almanac had been published since 1767. HMNAO produces astronomical data for a wide range of users, such as astronomers, mariners, aviators, surveyors, the military, Police, lawyers, religious groups, architects, schools, diary and calendar manufacturers, photographers and film crews.
In 1937, it became part of ROG and moved with it, when it moved away from Greenwich (and was renamed the Royal Greenwich Observatory) first to Herstmonceux Castle, near Hailsham in East Sussex in 1948, then to Cambridge in 1990. When the RGO closed in 1998 HMNAO was transferred to the Rutherford Appleton Laboratory, near Abingdon in Oxfordshire. In December 2006, HMNAO was transferred to the United Kingdom Hydrographic Office, which is based in Taunton in Somerset.