Wells Cathedral, formally the Cathedral Church of St Andrew, is a Church of England cathedral in Wells, Somerset, England. It is the seat of the bishop of Bath and Wells and the mother church of the diocese of Bath and Wells. There are daily Church of England services in the building, and in 2023 it was reported to receive over 300,000 visitors per year. The cathedral is a Grade I listed building. The cathedral precincts contain the Bishop's Palace and several buildings linked to its medieval chapter of secular canons, including the fifteenth-century Vicars' Close.

The earliest record of a church on the present site is a charter of 766. A bishopric was established in 909; however in 1090 the cathedral of the diocese was moved to Bath Abbey and remained there until Wells became co-cathedral in 1218. The remains of the tenth-century cathedral lie to the south of the present building, beneath the cloister. The present cathedral has a cruciform plan with a chapter house attached to the north and a cloister to the south, and is largely the result of two building campaigns which took place between c. 1180 to c. 1260 and c. 1285 to c. 1345. The western half of the cathedral, including the nave and western transepts, belongs primarily to the first building phase and is constructed in the Early English style of Gothic architecture. The east end, including the lady chapel, eastern transepts, chapter house, and central tower, belongs to the second phase and uses the Decorated Gothic style and retains much medieval stained glass. Two towers were added to the west front between 1385 and 1410 in the Perpendicular Gothic style, and the cloisters were remodelled in the same style between 1420 and 1508. The cathedral was restored over the course of the nineteenth and early twentieth centuries.

Wells has been called "unquestionably one of the most beautiful" and "most poetic" of English cathedrals. The architectural historian John Harvey sees it as Europe's first truly Gothic structure, breaking from the last constraints of the Romanesque style. The west front, which contains 300 sculpted figures, has been described by Harvey as the "supreme triumph of the combined plastic arts in England", however the architectural historian Nikolaus Pevsner described it as "spare", with "harsh uprights and horizontals [...] like steel scaffolding".

The earliest remains of a building on the site are of a late-Roman mausoleum, identified during excavations in 1980. An abbey church was built in Wells in 705 by Aldhelm, first bishop of the newly established Diocese of Sherborne during the reign of King Ine of Wessex. It was dedicated to St Andrew and stood at the site of the cathedral's cloisters, where some excavated remains can be seen. The font in the cathedral's south transept is from this church and is the oldest part of the present building. In 766 Cynewulf, King of Wessex, signed a charter endowing the church with eleven hides of land. In 909 the seat of the diocese was moved from Sherborne to Wells.

The first bishop of Wells was Athelm (909), who crowned King Æthelstan. Athelm and his nephew Dunstan both became Archbishops of Canterbury. During this period a choir of boys was established to sing the liturgy. Wells Cathedral School, which was established to educate these choirboys, dates its foundation to this point. There is, however, some controversy over this. Following the Norman Conquest, John de Villula moved the seat of the bishop from Wells to Bath in 1090. The church at Wells, no longer a cathedral, had a college of secular clergy.

The cathedral is thought to have been conceived and commenced in about 1175 by Reginald Fitz Jocelin, who died in 1191. Although it is clear from its size that from the outset, the church was planned to be the cathedral of the diocese, the seat of the bishop moved between Wells and the abbeys of Glastonbury and Bath, before settling at Wells. In 1197 Reginald's successor, Savaric FitzGeldewin, with the approval of Pope Celestine III, officially moved his seat to Glastonbury Abbey. The title of Bishop of Bath and Glastonbury was used until the Glastonbury claim was abandoned in 1219.

Savaric's successor, Jocelin of Wells, again moved the bishop's seat to Bath Abbey, with the title Bishop of Bath. Jocelin was a brother of Hugh (II) of Lincoln and was present at the signing of Magna Carta. Jocelin continued the building campaign begun by Reginald and was responsible for the Bishop's Palace, the choristers' school, a grammar school, a hospital for travellers and a chapel. He also had a manor house built at Wookey, near Wells. Jocelin saw the church dedicated in 1239 but, despite much lobbying of the Pope by Jocelin's representatives in Rome, he did not live to see cathedral status granted. The delay may have been a result of inaction by Pandulf Verraccio, a Roman ecclesiastical politician, papal legate to England and Bishop of Norwich, who was asked by the Pope to investigate the situation but did not respond. Jocelin died at Wells on 19 November 1242 and was buried in the choir of the cathedral; the memorial brass on his tomb is one of the earliest brasses in England. Following his death the monks of Bath unsuccessfully attempted to regain authority over Wells.

In 1245 the ongoing dispute over the title of the bishop was resolved by a ruling of Pope Innocent IV, who established the title as the "Bishop of Bath and Wells", which it has remained until this day, with Wells as the principal seat of the bishop. Since the 11th century the church has had a chapter of secular clergy, like the cathedrals of Chichester, Hereford, Lincoln and York. The chapter was endowed with 22 prebends (lands from which finance was drawn) and a provost to manage them. On acquiring cathedral status, in common with other such cathedrals, it had four chief clergy, the dean, precentor, chancellor and sacristan, who were responsible for the spiritual and material care of the cathedral.