Bass Brewery (/ˈbæs/) was founded in 1777 by William Bass in Burton-upon-Trent, Staffordshire, England. The main brand was Bass Pale Ale, once the highest-selling beer in the UK. By 1877, Bass had become the largest brewery in the world, with an annual output of one million barrels. Its pale ale was exported throughout the British Empire, and the company's red triangle became the UK's first registered trade mark.

Bass took control of a number of other large breweries in the early 20th century. In the 1960s it merged with Charrington United Breweries to become the largest UK brewing company, Bass Charrington. The brewing operations of the company were bought by Interbrew (now Anheuser-Busch InBev) in 2000, while the retail side (hotels and pubs) was renamed Six Continents plc. Because at the time Interbrew controlled a large portion of the UK beer market, the Competition Commission instructed Interbrew to sell the Bass brewery along with certain brands to Coors (now Molson Coors), while retaining the rights to the Bass brand. In 2010, it was widely reported that AB-InBev was attempting to sell the rights to the Bass brand in the UK for around £10 million to £15 million.

In the UK, draught Bass (4.4% ABV) has been brewed under contract in Burton by Marston's (formerly a relatively minor competitor) for AB-InBev since 2005, while bottled products are brewed at AB-InBev's own brewery in Samlesbury, Lancashire, for export. Bass is also brewed locally in the United States and Belgium. Bass Ale is a top ten premium canned ale in the UK, with 16,080 hectolitres sold in 2010.

Before establishing a brewery, William Bass transported ale for brewer Benjamin Printon. Bass sold this carrier business to the Pickford family, using the funds to establish Bass & Co Brewery in 1777 as one of the first breweries in Burton-upon-Trent.

Early in the company's history, Bass was exporting bottled beer around the world, serving the Baltic region through the port of Hull. Growing demand led his son Michael Thomas Bass (1760–1827), to build a second brewery in Burton in 1799 in partnership with John Ratcliff. The water from local boreholes became popular with brewers, with 30 operating there by the mid-19th century. His son, Michael Thomas Bass (1799–1884), succeeded on his father's death in 1827, renewed the Ratcliff partnership, brought in John Gretton, and created 'Bass, Ratcliff and Gretton'.

The opening of a railway through Burton in 1839 redoubled Burton's pre-eminence as a brewing town. In the mid-1870s, Bass, Ratcliff and Gretton accounted for one-third of Burton's output. A strong export business allowed Bass to boast that their product was available "in every country in the globe". By 1877, Bass was the largest brewery in the world, with an annual output of one million barrels. In the 1880s the brewery received unwanted publicity through the lifestyle of Frederick Gretton, son of John Gretton. Having worked for the company when a young man, he drifted away and developed a stable of racehorses. His 'Sterling' and 'Isonomy' were stars of the Turf. But Fred, as he was known, was also a heavy drinker and took a mistress, the teenage Fanny Lucy Radmall. In later life she would become a household name as Lucy, Lady Houston. When Fred died of drink in 1883 he left her £6,000 a year, much to the disgust of his family.

Following the death of the second Michael Thomas Bass in 1884, his son Michael Arthur Bass, later the 1st Baron Burton, took the reins. Both Michael Thomas Bass and his son Lord Burton were philanthropically inclined, making extensive charitable donations to the towns of Burton and Derby. The annual Bass excursions, laid on by the firm for its employees, were the largest operation of its type in the world by a private company. The brewer became a public limited company in 1888.

Bass' No. 1 Ale was the first beer to be marketed as barley wine, around 1870.