Derry, officially Londonderry, is the second-largest city in Northern Ireland, and the fifth-largest on the island of Ireland. Located in County Londonderry, the city now covers both banks of the River Foyle. Cityside and the old walled city being on the west bank and Waterside on the east, with two road bridges and one footbridge crossing the river in-between.

The population of the city was 85,279 in the 2021 census, while the Derry Urban Area had a population of 105,066 in 2011. The district administered by Derry City and Strabane District Council contains both Londonderry Port and City of Derry Airport. Derry is close to the border with County Donegal, with which it has had a close link for many centuries. The person traditionally seen as the founder of the original Derry is Saint Colmcille, a holy man from Tír Chonaill, the old name for almost all of modern County Donegal, of which the west bank of the Foyle was a part before 1610.

In 2013, Derry was the inaugural UK City of Culture, having been awarded the title in 2010.

Despite the official name, the city is commonly known as Derry, which is an anglicisation of the Irish Daire or Doire, which translates as 'oak-grove/oak-wood'. The name derives from the settlement's earliest references, Daire Calgaich ('oak-grove of Calgach'). The name was changed from Derry in 1613 during the Plantation of Ulster to reflect the establishment of the city by the London guilds.

Derry has been used in the names of the local government district and council since 1984, when the council changed its name from Londonderry City Council to Derry City Council. This also changed the name of the district, which had been created in 1973 and included both the city and surrounding rural areas. In the 2015 local government reform, the district was merged with the Strabane district to form the Derry City and Strabane district, with the councils likewise merged.

According to the city's royal charter of 10 April 1662, the official name is Londonderry. This was reaffirmed in a High Court decision in 2007.

The 2007 court case arose because Derry City Council wanted clarification on whether the 1984 name change of the council and district had changed the official name of the city and what the procedure would be to effect a name change. The court clarified that Londonderry remained the official name and that the correct procedure to change the name would be via a petition to the Privy Council. Derry City Council afterwards began this process and was involved in conducting an equality impact assessment report (EQIA). Firstly it held an opinion poll of district residents in 2009, which reported that 75% of Catholics and 77% of Nationalists found the proposed change acceptable, compared to 6% of Protestants and 8% of Unionists. The EQIA then held two consultative forums and solicited comments from the general public on whether or not the city should have its name changed to Derry. A total of 12,136 comments were received, of which 3,108 were broadly in favour of the proposal, and 9,028 opposed it. On 23 July 2015, the council voted in favour of a motion to change the official name of the city to Derry and to write to Mark H. Durkan, the Northern Irish Minister for the Environment, to ask how the change could be effected.

The name Derry is preferred by nationalists and it is broadly used throughout Northern Ireland's Catholic community, as well as that of the Republic of Ireland, whereas many unionists prefer Londonderry; however, in everyday conversation Derry is used by most Protestant residents of the city. Linguist Kevin McCafferty argues that "It is not, strictly speaking, correct that Northern Ireland Catholics call it Derry, while Protestants use the Londonderry form, although this pattern has become more common locally since the mid-1980s, when the city council changed its name by dropping the prefix". In McCafferty's survey of language use in the city, "only very few interviewees—all Protestants—use the official form".