Christchurch (/ˈkraɪs.tʃɜːrtʃ/ ^ⓘ; Māori: Ōtautahi) is the largest city in the South Island and the second-largest city by urban area population in New Zealand. Christchurch has an urban population of 407,800, and a metropolitan population of 556,500. It is located in the Canterbury Region, near the centre of the east coast of the South Island, east of the Canterbury Plains. It is located near the southern end of Pegasus Bay, and is bounded to the east by the Pacific Ocean and to the south by the ancient volcanic complex of the Banks Peninsula. The Avon River / Ōtākaro winds through the centre of the city, with a large urban park along its banks. With the exception of the Port Hills, it is a relatively flat city, on an average around 20 m (66 ft) above sea level. Christchurch has a reputation for being an English city, with its architectural identity and nickname the 'Garden City' due to similarities with garden cities in England, but also has a historic Māori heritage. Christchurch has a temperate oceanic climate with regular moderate rainfall.

The area of modern-day greater Christchurch was first inhabited by the historic Māori iwi Waitaha in the mid-thirteenth century. Waitaha, who occupied the swamplands with patchworks of marshland, were invaded by Kāti Māmoe in the sixteenth century, and then were absorbed by Kāi Tahu a century later. Ōtautahi was inhabited seasonally, and a major trading centre was established at Kaiapoi Pā. British colonial settlement began in the mid-nineteenth century. The First Four Ships were chartered by the Canterbury Association and brought the Canterbury Pilgrims from Britain to Lyttelton Harbour in 1850. It became a city by letters patent on 31 July 1856, making it officially the oldest established city in New Zealand. Christchurch was heavily industrialised in the early 20th century, with the opening of the Main South Line railway and the development of state housing saw rapid growth in the city's economy and population.

Christchurch has strong cultural connections with its European elements and architectural identity. Christchurch is also home to a number of performing arts centres and academic institutions (including the University of Canterbury). Christchurch has hosted numerous international sporting events, notably the 1974 British Commonwealth Games at the purpose-built Queen Elizabeth II Park. The city has been recognised as an Antarctic gateway since 1901, and is nowadays one of the five Antarctic gateway cities hosting Antarctic support bases for several nations. Christchurch is served by the Christchurch Airport in Harewood, the country's second-busiest airport.

The city suffered a series of earthquakes from September 2010, with the most destructive occurring on 22 February 2011, in which 185 people were killed and thousands of buildings across the city suffered severe damage, with many central city buildings collapsing, leading to ongoing recovery and rebuilding projects. Christchurch later became the site of the worst terrorist attack in New Zealand history targeting two mosques on 15 March 2019.

The name Christchurch was adopted at the first meeting of the Canterbury Association on 27 March 1848. The reason it was chosen is not known with certainty, but the most likely reason is it was named after Christ Church, Oxford, the alma mater of many members of the association, including John Robert Godley. Christ Church college had similarities with the planned new city, including its own cathedral, the smallest in England. Other possibilities are that it was named for Christchurch, Dorset, or for Canterbury Cathedral. Many of the early colonists did not like the name, preferring instead the name Lyttelton, but the Colonists' Council resolved to stick with the name of Christchurch in 1851, because it had been used by surveyors and distinguished the settlement from the port.

The Māori name for modern-day Christchurch is Ōtautahi, meaning 'the place of Tautahi'. It was adopted as the Māori name for the city in the 1930s. Ōtautahi precisely refers to a specific site by the Avon River / Ōtākaro in Central Christchurch. The site was a seasonal food-gathering place of Ngāi Tahu chief Te Pōtiki Tautahi. A different account claims the Tautahi in question was the son of the Port Levy chief Huikai. Prior to that, Ngāi Tahu generally referred to the Christchurch area as Karaitiana, a transcription of Christchurch in the Māori language.

"ChCh" is commonly used as an abbreviation of Christchurch. In New Zealand Sign Language, Christchurch is signed with two Cs.

Prior to European occupation of the modern-day greater Christchurch area, the land was originally swampland with patchworks of marshland, grassland, scrub and some patches of tall forest of mostly kahikatea, mataī and tōtara. The inner coastal sand dunes were covered in hardier scrub bush, including akeake, taupata, tūmatakuru, ngaio, carmichaelia, and coprosma. Christchurch was rich in birdlife, but European colonisers burned forests to create pasture and introduced predators. This led to local extinction of many species of native birds.