Scunthorpe (/ˈskʌnθɔːrp/) is an industrial town in Lincolnshire, England, and the county's third most populous settlement after Lincoln and Grimsby, with a population of 81,286 in 2021. It is the administrative centre and largest settlement of the North Lincolnshire district. Scunthorpe lies north of Lincoln and is between Grimsby to the east and Doncaster to the west, while Hull is to the north-east via the Humber Bridge.

The town appears in the Domesday Book of 1086 as Escumesthorpe, which is from the Old Norse Skumasþorp meaning "Skuma's homestead", a site which is believed to be in the town centre, close to Market Hill. Today Skuma’s homestead means ‘A secondary settlement, a dependent outlying farmstead or hamlet’.

Scunthorpe as a town came into existence due to the exploitation of the local ironstone which began in 1859; iron production commenced in 1864, steel smelting in 1891.

Scunthorpe's population grew from 1,245 in 1851 to 11,167 in 1901 and 45,840 in 1941. The boundaries of Scunthorpe expanded to include the former villages of Bottesford, Yaddlethorpe, Frodingham, Crosby, Brumby and Ashby. Scunthorpe became an urban district in 1891, merged as 'Scunthorpe, Brumby and Frodingham Urban District' in 1919, and became a municipal borough in 1936. Scunthorpe was originally dominated, socially, politically and culturally, by Rowland Winn, the most significant landowner in the district. By the First World War local working class culture, drawing on trade unions and the Labour Party had emerged to challenge the Conservative Party's hegemony.

Scunthorpe is located close to an outcrop of high-lime-content ironstone (~25% iron average) from a seam of the Lias Group strata which dates from the Early Jurassic period and runs north–south through Lincolnshire. Ironstone was mined by open cast methods from the 1850s onwards, and by underground mining from the late 1930s. In the 1970s the steel industry in Scunthorpe began to use of ores imported from outside the UK with higher iron content. Underground mining in the area ceased in 1981.

Scunthorpe was close to the epicentre (at Middle Rasen) of the 2008 Market Rasen earthquake, the second largest earthquake experienced in the British Isles, which had a magnitude of 5.2. Significant shocks were felt in Scunthorpe and the North Lincolnshire vicinity. The main 10-second quake, which struck at 00:56 GMT on 27 February 2008, at a depth of 9.6 mi (15.4 km), was second only to a 1984 quake, with a magnitude of 5.4, in North Wales.

Scunthorpe forms an unparished area located within the borough and unitary authority of North Lincolnshire. The town forms six of the borough's seventeen wards, namely Ashby, Brumby, Crosby & Park, Frodingham, Kingsway with Lincoln Gardens and Town. The Scunthorpe wards elect 16 of the borough's 43 councillors. As of 2018, 26 are members of the Conservative party, and 13 are members of the Labour party. The councillors form the charter trustees of the Town of Scunthorpe and they continue to elect a town mayor.

North Lincolnshire Council was based in Scunthorpe Civic Centre off Ashby Road (former A159) next to Festival Gardens. It was designed by Charles B. Pearson, Son and Partners and was completed in 1962. It was the home of Scunthorpe Borough Council until 1996. It was named Pittwood House after Edwin Pittwood, a local Labour politician, who worked in the opencast ironstone workings near Normanby Park.