Selsdon is an area in South London, England, located in the London Borough of Croydon, in the ceremonial county of Greater London. Prior to 1965 it was in the historic county of Surrey. It now has the character of a suburb and sits at a high elevation, bordering downland.

The London Borough of Croydon is a London borough in south London, part of Outer London. It covers an area of 87 km2 (33.6 sq mi). It is the southernmost borough of London. At its centre is the historic town of Croydon from which the borough takes its name; while other urban centres include Coulsdon, Purley, South Norwood, Norbury, New Addington, Selsdon and Thornton Heath. Croydon is mentioned in Domesday Book, and from a small market town has expanded into one of the most populous areas on the fringe 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. Its population is 390,719, making it the largest London borough and sixteenth largest English district.