Crumlin (Irish: Croimghlinn, meaning 'Crooked Glen') is a Southside suburb of Dublin, Ireland. Formerly a rural area, it became heavily built up from the early 20th century onwards. Crumlin is the site of Ireland's largest children's hospital, Our Lady's Children's Hospital.

The population of all electoral divisions labelled as Crumlin was 19,287 as of the 2022 census. Crumlin is in a townland and civil parish of the same name.

Crumlin covers the area from the Stannaway road near the KCR (Kimmage Cross Roads) to Sundrive Road and Crumlin Cross at the Ashleaf Shopping Centre to Crumlin's village core and the Drimnagh Road, to Bunting Road, Crumlin Road then along the Grand Canal from Rialto Bridge to Sally's Bridge. It is situated near to the city centre, on the Southside of Dublin city. Neighbouring areas include Walkinstown, Perrystown, Drimnagh, Terenure, and Kimmage. Crumlin is contained within postal district Dublin 12.

Crumlin gets its name from the "crooked valley" known as Lansdowne Valley. The valley was formed by glacial erosion in the distant past and is now bisected by the River Camac. The valley is situated in front of Drimnagh.^{[citation needed]}

During the medieval period, Dublin was surrounded by manorial settlements, each comprising a manor house, church and graveyard, farmland and cottages. These settlements grew into a network of villages around Dublin, creating stability and continuity of location. Crumlin village developed as an Anglo-Norman settlement soon after the Norman Conquest in 1170 (although the circular configuration of the old graveyard of Saint Mary's in the village suggests pre-Norman associations), and has survived through the centuries to become the village of today. The Old Saint Mary's Church stands on the site of a 12th-century church of the same dedication, and a succession of churches occupied the site down through the centuries to the present day. In 1193, John, Lord of Ireland, gave the Crumlin church to form one prebend for the collegiate church of Saint Patrick. When the main body of the present old church was rebuilt in 1817, the old tower of much earlier origin was preserved.

Crumlin, along with Saggart, Newcastle, Lyons and Esker (Lucan), was constituted a royal manor by King John sometime before the end of his reign in 1216. The English noble families of the time had strong links with Ireland, particularly in Leinster. For example, William Fitz John of Harptree was a lord of some significance in Somerset and likely to have served in Ireland under King John. At the beginning of the reign of King Henry III, Fitz John acquired the custody of the lands of William de Carew and held the royal manor of Crumlin, although he did not establish family roots in Ireland.

From 1609 until the 19th century, Edmund Purcell and then the Purcell family leased land in Crumlin. John Brice, Mayor of Dublin in 1605, lived in Crumlin.

Crumlin House was said to have been constructed by Joseph Deane in the area in the early 18th century incorporating elements of an earlier manor house. The house was later owned by members of the Purcell family. It still stands as of 2023 incorporated into the structure of the Salesian provincial house.