The London Borough of Harrow is a London borough in northwest London, England; it forms part of Outer London. It borders four other London boroughs – Barnet to the east of ancient Watling Street, Brent to the southeast, Ealing to the south and Hillingdon to the west – plus the Hertfordshire districts of Three Rivers and Hertsmere to the north. The local authority is Harrow London Borough Council. The London borough was formed in 1965, based on boundaries that had been established in 1934. The borough is made up of three towns: Harrow, Pinner and Stanmore, but also includes western parts of Edgware.

The London Borough of Barnet is a local authority area on the northern outskirts of London. The borough was formed in 1965 from parts of the ceremonial counties of Middlesex and Hertfordshire. It is the second largest London borough by population with 389,344 inhabitants as of 2021, also making it the 17th largest district in England. The borough covers an area of 86.74 square kilometres (33 sq mi), the fourth highest of the 32 London boroughs, and has a population density of 45.8 people per hectare, which ranks it 25th.