Welwyn Hatfield is a local government district with borough status in the county of Hertfordshire, England. Its council is based in Welwyn Garden City. The borough borders Hertsmere, St Albans, North Hertfordshire, East Hertfordshire, Broxbourne, and the London Borough of Enfield.

The borough includes the two towns of Welwyn Garden City and Hatfield, along with numerous smaller settlements from Woolmer Green in the north to Cuffley in the south. The borough has six railway stations on the Great Northern Railway; five being on the main line and one on the Hertford loop line. The Digswell Viaduct is a local landmark. The A1 road passes through the borough.

Much of the borough lies within the Metropolitan Green Belt which surrounds London. Welwyn Garden City is notable as being one of only two Garden Cities in the country, and is uniquely both a Garden City and a designated New Town. The University of Hertfordshire has its main campus at Hatfield.

Welwyn Hatfield was created on 1 April 1974 under the Local Government Act 1972, covering the area of three former districts, which were all abolished at the same time:^[2]

• Hatfield Rural District
• Welwyn Garden City Urban District
• Welwyn Rural District

The new district was named Welwyn Hatfield.^[3] From 1974 to 2006 the council was called Welwyn Hatfield District Council. The council petitioned for borough status in 2005, allowing the chair of the council to take the title of mayor. The petition was agreed to by the Privy Council and a charter conferring borough status was issued which took effect on 22 May 2006, when John Hawkins was appointed the first mayor and the council's name changed to Welwyn Hatfield Borough Council.^[4]

Hertfordshire has a two-tier structure of local government, with the ten district councils (including Welwyn Hatfield Borough Council) providing district-level services, and Hertfordshire County Council providing county-level services.^[8]

The council is based at the Council Offices on The Campus in the centre of Welwyn Garden City, which it inherited from the old Welwyn Garden City Urban District Council. The building was completed in 1937.^[16]

Welwyn Hatfield contains eight civil parishes. The town of Welwyn Garden City is an unparished area. The parishes are:

Since the last boundary changes in 2016 the council has comprised 48 councillors representing 16 wards, each of which elects three councillors. Elections are held three years out of every four, electing one councillor from each ward each time. Elections to Hertfordshire County Council are held in the fourth year of the cycle when there are no borough council elections.^[17]