The London Borough of Croydon is a London borough in South London, England and is part of Outer London. It covers an area of 87 km2 (33.6 sq mi) and is the largest London borough by population. It is the southernmost borough of London. The borough is now one of London's leading business, financial and cultural centres, and its influence in entertainment and the arts contribute to its status as a major metropolitan centre.

At its centre is the historic town of Croydon from which the borough takes its name. Croydon is mentioned in the Domesday Book, and from a small market town has expanded into one of the most populous areas on the fringe of London. Croydon is the civic centre of the borough and houses the largest office and retail centre in the south east of England outside Central London.

Croydon Council and its predecessor Croydon Corporation unsuccessfully applied for city status in 1954, 2000 and 2002. The area is currently going through a large regeneration project called Croydon Vision 2020 which is predicted to attract more businesses and tourists to the area as well as backing Croydon's bid to become London's Third City. Since 2003 Croydon has been certified as a Fairtrade borough by the Fairtrade Foundation. It was the first London Borough to have Fairtrade status which is awarded on certain criteria.