St Stephen Walbrook is a church in the City of London, part of the Church of England's Diocese of London. The present domed building was erected to the designs of Sir Christopher Wren following the destruction of its medieval predecessor in the Great Fire of London in 1666. It is located in Walbrook, next to the Mansion House, and near to Bank and Monument Underground stations.

The original church of St Stephen stood on the west side of the street today known as Walbrook and on the east bank of the Walbrook, once an important fresh water stream for the Romans running south-westerly across the City of London from the City Wall near Moorfields to the Thames. The original church is thought to have been built directly over the remains of a Roman Mithraic Temple following a common Christian practice of hallowing former heathen sites of worship.

The church was moved to its present higher site on the other side of Walbrook Street, still on the east side of the River Walbrook (later diverted and concealed in a brick culvert running under Walbrook Street and Dowgate Hill on a straightened route to the Thames), in the 15th century. In 1429 Robert Chichele, acting as executor of the will of the former Lord Mayor, William Standon, had bought a piece of land close to the Stocks Market (on the site of the later Mansion House) and presented it to the parish. Several foundation stones were laid at a ceremony on 11 May 1429, and the church was consecrated ten years later, on 30 April 1439. At 125 feet (38 m) long and 67 feet (20 m) wide, it was considerably larger than the present building.

The church was destroyed in the Great Fire of London in 1666. It contained a memorial to the composer John Dunstaple. The wording of the epitaph had been recorded in the early 17th century, and was reinstated in the church in 1904, some 450 years after his death.^{[citation needed]} The nearby church of St Benet Sherehog, also destroyed in the Great Fire, was not rebuilt; instead its parish was united with that of St Stephen.

The present building was constructed between 1672 and 1679 to a design by Sir Christopher Wren, at a cost of £7,692. The mason was Thomas Strong brother of Edward Strong the Elder and the spire is by Edward Strong the Younger. It is rectangular in plan, with a dome and an attached north west tower. Entry to the church is up a flight of sixteen steps, enclosed in a porch attached to the west front. Wren also designed a porch for the north side of the church. This was never built, but there once was a north door, which was bricked up in 1685, as it let in the offensive smells from the slaughterhouses in the neighbouring Stocks Market. The walls, tower, and internal columns are made of stone, but the dome is of timber and plaster with an external covering of copper

The 63 feet (19 m) high dome is based on Wren's original design for St Paul's, and is centred over a square of twelve columns of the Corinthian order. The circular base of the dome is not carried, in the conventional way, by pendentives formed above the arches of the square, but on a circle formed by eight arches that spring from eight of the twelve columns, cutting across each corner in the manner of the Byzantine squinch. This all contributes to create what many consider to be one of Wren's finest church interiors. Sir Nikolaus Pevsner lists it as one of the ten most important buildings in England.

The contemporary carved furnishings of the church, including the altarpiece and Royal Arms, the pulpit and font cover, are attributed to the carpenters Thomas Creecher and Stephen Colledge, and the carvers William Newman and Jonathan Maine.

In 1760 a new organ was provided by George England.