Grubb Parsons (legally 'Sir Howard Grubb, Parsons and Co. Ltd.') was a historic manufacturer of telescopes, active in the 19th and 20th centuries. They built numerous large research telescopes, including several that were (at the time of construction) the largest in the world of their type.

It was founded in 1833 by Thomas Grubb as the Grubb Telescope Company, located in Dublin. Control of the company passed to his son Howard Grubb in the 1860s. They produced dozens of telescopes, including some of the largest of the 19th century, such as the 48-inch (1.2 m) Great Melbourne Telescope (a reflecting telescope) in 1868, a 27-inch (0.69 m) refractor for the Vienna Observatory in 1878, and the Greenwich 28 inch refractor in 1893. Leading up to and during the First World War (1914-18) the company produced periscopes for submarines and moved to St Albans in 1918.

In 1925 the company was purchased by Charles Algernon Parsons, renamed Grubb Parsons, and moved to Newcastle upon Tyne. In the 20th century they produced large research telescopes including the Isaac Newton Telescope (1965), Anglo-Australian Telescope (1965) and UK Infrared Telescope (1979). Their final project was the William Herschel Telescope in 1985, after which the company shut down.

The Grubb Telescope Company was founded in Dublin by the Irish engineer Thomas Grubb in 1833. He ran a precision engineering company whose cast iron products included billiard tables and printing presses for banknotes. Grubb had a personal interest in optics and was a friend of the Irish astronomer Thomas Romney Robinson. His first foray into telescope construction was his own 9-inch (230 mm) refractor, which he operated as a public observatory in Portobello, Dublin, as a visitor attraction.

The company's first order was the mount for the 13.3-inch (340 mm) telescope at Markree Observatory, completed in 1834 as the largest refracting telescope in the world. Edward Joshua Cooper, the owner of Markree Castle, had purchased the optics from Robert-Aglaé Cauchoix of Paris and commissioned Grubb (on Robinson's recommendation) to construct the mechanical supports. Grubb provided an equatorial mount that could track targets automatically using a clock drive; although this was not the first telescope with an equatorial mount, it was far larger than previous examples. This was followed in 1835 by a 15-inch (380 mm) reflecting telescope for Armagh Observatory (run by Robinson), which used the Cassegrain layout and another equatorial mount. The combination of an equatorial mount with the Cassegrain layout was innovative and had not been used on large telescopes before; it was widely adopted thereafter.

Orders from outside Ireland soon followed, including the 6.7-inch (170 mm) Sheepshanks equatorial refractor for the Royal Observatory, Greenwich (London, 1838) and a 6.0-inch (150 mm) refractor for the United States Military Academy (West Point, 1840), both using lenses that had been produced by Cauchoix in Paris. In the 1850s and 60s, the company also produced compound microscopes.

With Thomas Grubb approaching retirement, in 1865 he was joined in managing the company by his son Howard Grubb. Thomas Grubb retired in 1868 and died in 1878. Howard Grubb solidified the company's reputation for high-quality optical instruments, and was knighted in 1887.

The Grubbs contributed to the early development of astronomical spectroscopy by producing various spectroscopes. Surviving examples include spectroscopes with two and six prisms (the latter completed in 1867).