Valby ([vælpyˀ] ^ⓘ) is one of the 10 official districts of Copenhagen Municipality, Denmark. It is in the southwestern corner of Copenhagen Municipality, and has a mixture of different types of housing. This includes apartment blocks, terraced housing, areas with single-family houses and allotments, plus the remaining part of the old Valby village, around which the district has formed, intermingled with past and present industrial sites.

Valby Hill marks the boundary between Valby and the more central and urban neighbouring Vesterbro district. The expression "west of Valby Hill" is in Danish often used as a metonym for "the provinces" or "outside Copenhagen". Separated from the rest of Copenhagen by Vestre Cemetery, Denmark's largest cemetery, towards Vesterbro/Kongens Enghave and Søndermarken-Frederiksberg Gardens towards Frederiksberg, the Carlsberg brewery site, and areas of low density, Valby retains a certain air of 'independence', or isolation, even today. With the progressing redevelopment of the Carlsberg area into a new lively, high-density neighbourhood, this is likely to change. Other former industrial sites are also under redevelopment and Valby is today one of the districts in Copenhagen with the fastest growing population.

Valby covers an area of 9,23 km² and has a population of 66.435, giving a population density of 7.197 per km². The district is bounded by Kongens Enghave and Vesterbro to the east, Frederiksberg to the north, Vanløse to the north-east and Hvidovre Municipality to the west, while Kalvebod Beach, the shallow-watered area just south of Copenhagen Harbour, separates it from the island of Amager to the south.

The most distinctive geographical features of the district are Valby Hill in its north-eastern corner and Harrestrup Å which marks its western boundary. Valby also borders on Damhus Lake in its extreme north-western corner.

The Danshøj tumulus, along with many other archeological finds in the area, provides evidence that the Valby area has been inhabited since ancient times. Modern Valby has developed around the two villages of Valby and Vigerslev. The first recorded mention of the name Valby is from 1186, as Walbu, but the history of both settlements probably goes back considerably longer. Valby means "village/house on the plain". In the early Middle Ages both villages came under Utterslev, a Crown estate which included most of the area around Havn, the small market town which later became Copenhagen.

In 1167, Valdemar I granted both Havn and the Utterslev estate to the Bishop's Seat of Roskilde but in 1417 the villages came under the Crown once again when King Eric VII made Copenhagen a royal possession.

Both during the civil war leading up to the Reformation (1533–1536) and during the Assault on Copenhagen in the Second Northern War, Valby was faced with almost complete destruction (1658–60), leading to deep poverty for the communities.

In 1682, Valby had 13 farms and 25 houses with no more land than a modest garden. The produce from this intensely cultivated area was, in fierce competition with the Amager farmers, sold on the market at Amagertorv in Copenhagen, where King Christian IV had granted the Valby farmers trading privileges.