The true name of the city of Derry or Londonderry in Northern Ireland is a subject of dispute between nationalists (mostly Catholic) and unionists (most of whom are Protestant), with nationalists calling it Derry, and unionists, Londonderry. Although many unionists will call it Derry in casual conversation, they generally insist on calling it Londonderry during political discourse; the reverse is not true of nationalists. The most visible sign of this dispute to the visitor is in the road signage; those pointing to the town from within the Republic refer to it as "Derry", whilst across the border it is written as "Londonderry". It is not uncommon to see vandalised road signs - the "London" part of the name spray painted over on "Londonderry" road signs by nationalists, and occasionally added to "Derry" signs by unionists.

The name Derry is an anglicisation of the Irish name, Doire ("oak grove"). When a new walled city was built by The Honourable The Irish Society across the River Foyle from the old site of the town, using donations from the livery companies of the City of London during the Plantation of Ulster by English and Scottish settlers, it was renamed and granted a royal charter as the City of Londonderry.

Irish nationalists, however, do not accept the change of name. The local authority is controlled by nationalist parties, and has officially changed its name to Derry City Council. The name of the city is still specified by its charter as Londonderry, and many unionists continue to call it Londonderry. The council has the power to apply to the Secretary of State for Northern Ireland to change the city's name officially, but has not done so.

A suggested compromise wording of "Derry/Londonderry" (read "Derry stroke Londonderry") has given rise to the ironic local usage "Stroke City". Gerry Anderson, a local radio presenter who espoused this term, became known briefly as "Gerry/Londongerry". Another locally-used method of partly circumventing this name problem is to write "L'derry" or "L-Derry".