Brighton (/ˈbraɪtən/ ^ⓘ BRY-tən) is a seaside resort in the city of Brighton and Hove, East Sussex, England, 47 miles (76 km) south of London. Archaeological evidence of settlement in the area dates back to the Bronze Age, Roman and Anglo-Saxon periods. The ancient settlement of "Brighthelmstone" was documented in the Domesday Book (1086). The town's importance grew in the Middle Ages as the Old Town developed, but it languished in the early modern period, affected by foreign attacks, storms, a suffering economy and a declining population. Brighton began to attract more visitors following improved road transport to London and becoming a boarding point for boats travelling to France. The town also developed in popularity as a health resort for sea bathing as a purported cure for illnesses.

In the Georgian era, Brighton developed as a highly fashionable seaside resort, encouraged by the patronage of the Prince Regent, later King George IV, who spent much time in the town and constructed the Royal Pavilion in the Regency era. Brighton continued to grow as a major centre of tourism following the arrival of the railways in 1841, becoming a popular destination for day-trippers from London. Many of the major attractions were built in the Victorian era, including the Grand Hotel, the Hilton Brighton Metropole, the Palace Pier and the West Pier. The town continued to grow into the 20th century, expanding to incorporate more areas into the town's boundaries before joining Hove to form the unitary authority of Brighton and Hove in 1997, which was granted city status in 2000. Today, Brighton and Hove district has a resident population of about 283,870 and the wider Brighton and Hove conurbation has a population of 474,485 (2011 census).

Brighton's location has made it a popular destination for tourists, renowned for its diverse communities, shopping areas, large and vibrant cultural, music and arts scene, and its large LGBT population, leading to its recognition as the "unofficial gay capital of the UK". As of the 2021 census, 10.7% of the population of Brighton and Hove over the age of 18 identify as gay, lesbian or bisexual, the highest percentage in the entire UK. Brighton has been called the UK's "hippest city", as well as "the happiest place to live in the UK".

The earliest attestation of Brighton's name is Bristelmestune, recorded in the Domesday Book. Although more than 40 variations have been documented, Brighthelmstone (or Brighthelmston) was the standard rendering between the 14th and 18th centuries.

Brighton was originally an informal shortened form, first seen in 1660; it gradually supplanted the longer name and was in general use from the late 18th century, although Brighthelmstone remained the town's official name until 1810. The name is of Anglo-Saxon origin. Most scholars believe that it derives from Beorthelm + tūn—the homestead of Beorthelm, a common Old English name associated with villages elsewhere in England. The tūn element is common in Sussex, especially on the coast, although it occurs infrequently in combination with a personal name. An alternative etymology taken from the Old English words for 'stony valley' is sometimes given but has less acceptance. Brighthelm gives its name to, among other things, a church, a pub in Brighton, some halls of residence at the University of Sussex. Writing in 1950, historian Antony Dale noted that unnamed antiquaries had suggested an Old English word brist or briz, meaning 'divided', could have contributed the first part of the historic name Brighthelmstone. The town was originally split in half by the Wellesbourne, a winterbourne which was culverted and buried in the 18th century.

Brighton has several nicknames. Poet Horace Smith called it "The Queen of Watering Places", and "Old Ocean's Bauble". Novelist William Makepeace Thackeray referred to "Doctor Brighton", calling the town "one of the best of Physicians". "London-by-the-Sea" is well-known, reflecting Brighton's popularity with Londoners as a day-trip resort, a commuter dormitory and a desirable destination for those wanting to move out of the metropolis. "The Queen of Slaughtering Places", a pun on Smith's description, became popular when the Brighton trunk murders came to the public's attention in the 1930s. The mid-19th-century nickname "School Town" referred to the remarkable number of boarding, charity and church schools in the town at the time.

The first settlement in the Brighton area was Whitehawk Camp, a Neolithic encampment on Whitehawk Hill which has been dated to between 3500 BC and 2700 BC. It is one of six causewayed enclosures in Sussex. Archaeologists have only partially explored it, but have found numerous burial mounds, tools and bones, suggesting it was a place of some importance. There was also a Bronze Age settlement at Coldean. Brythonic Celts arrived in Britain in the 7th century BC, and an important Brythonic settlement existed at Hollingbury Castle on Hollingbury Hill. This Celtic Iron Age encampment dates from the 3rd or 2nd century BC and is circumscribed by substantial earthwork outer walls with a diameter of c. 1,000 ft (300 m). Cissbury Ring, roughly 10 mi (16 km) from Hollingbury, is suggested to have been the tribal "capital".

Later, there was a Roman villa at Preston Village, a Roman road from London ran nearby, and much physical evidence of Roman occupation has been discovered locally. From the 1st century AD, the Romans built a number of villas in Brighton and Romano-British Brythonic Celts formed farming settlements in the area. After the Romans left in the early 4th century AD, the Brighton area returned to the control of the native Celts. Anglo-Saxons then invaded in the late 5th century AD, and the region became part of the Kingdom of Sussex, founded in 477 AD by king Ælle.