Guildhall is a municipal building in the City of London, England. It is off Gresham and Basinghall streets, in the wards of Bassishaw and Cheap. The current building dates from the 15th century; however documentary evidence suggests that a guildhall had existed at the site since at least the early 12th century. The building has been used as a town hall for several hundred years, and is still the ceremonial and administrative centre of the City of London and its Corporation. It should not be confused with London's City Hall, the administrative centre for Greater London in Canning Town. The term "Guildhall" refers both to the whole building and to its main room, which is a medieval great hall. It is a Grade I-listed building.

During the Roman period, the Guildhall was the site of the London Roman Amphitheatre, rediscovered as recently as 1988. It was the largest in Roman Britain, partial remains of which are on public display in the basement of the Guildhall Art Gallery, and the outline of whose arena is marked with a black circle on the paving of the courtyard in front of the hall. The siting of the Anglo-Saxon Guildhall here was probably due to the amphitheatre's remains. Excavations by Museum of London Archaeology at the entrance to Guildhall Yard exposed remains of the great 13th-century gatehouse built directly over the southern entrance to the Roman amphitheatre, which raises the possibility that enough of the Roman structure survived to influence the siting not only of the gatehouse and Guildhall itself but also of the church of St Lawrence Jewry whose strange alignment may shadow the elliptical form of the amphitheatre beneath.

The first documentary reference to a London Guildhall is dated 1127 or 1128; archaeologists have also discovered foundations dating to around that time. Legend describes the Guildhall site as being the location of the palace of Brutus of Troy, who according to Geoffrey of Monmouth's Historia Regum Britanniae (1136) is said to have founded a city on the banks of the River Thames, known as Troia Nova, or New Troy.

The great hall is believed to be on a site of an earlier guildhall (one possible derivation for the word "guildhall" is the Anglo-Saxon "gild", meaning payment, with a "gild-hall" being where citizens would pay their taxes). Possible evidence for this derivation may be in a reference to John Parker, the sergeant of "Camera Guyhalde", London, in 1396.

Construction began on the current building in 1411 and was completed in 1440 under the supervision of John Croxton.

The Great Hall did not completely escape damage in the Great Fire of London in 1666; it was partially restored (with a flat roof) in 1670. The present grand entrance (the east wing of the south front), in "Hindoostani Gothic", was added in 1788 by George Dance. A more extensive restoration than that in 1670 was completed in 1866 by the City of London architect Sir Horace Jones, who added a new timber roof in close keeping with the original hammerbeam ceiling. This replacement was destroyed during the Second Great Fire of London on the night of 29/30 December 1940, the result of a Luftwaffe fire-raid. It was replaced in 1954 during works designed by Sir Giles Gilbert Scott, though the original hammerbeam design was not retained. The large, seated sculpture of Winston Churchill by Oscar Nemon, which was cast by H. H. Martyn & Co., was unveiled by Churchill in 1955.

Trials at the Guildhall have included those of Anne Askew (the Protestant martyr), Thomas Cranmer (Archbishop of Canterbury) and Lady Jane Grey ("the Nine Days' Queen") as well as Henry Garnet (executed for his complicity in the Gunpowder Plot of 1605).

The 1783 hearing of the infamous Zong case, the outcome of which focused public outrage about the transatlantic slave trade, also took place at Guildhall. On 16 November 1848, the pianist Frédéric Chopin made his last public appearance on a concert platform there. The marathon route of the 2012 Summer Olympics passed through Guildhall Yard.