Kings Langley is a village, former manor and civil parish in Hertfordshire, England, 21 miles (34 kilometres) north-west of Westminster in the historic centre of London and to the south of the Chiltern Hills. It now forms part of the London commuter belt. The village is divided between two local government districts by the River Gade with the larger western portion in the Borough of Dacorum and smaller part, to the east of the river, in Three Rivers District. It was the location of Kings Langley Palace and the associated King's Langley Priory, of which few traces survive.

It is 2 mi (3 km) situated south of Hemel Hempstead and 2 mi (3 km) north of Watford.

The earliest mention in surviving documents of the manor of Langalega is in a Saxon charter dated circa 1050. It appears as Langelai in the Domesday Book of 1086, and is recorded as Langel' Regis ("Langley of the King") in 1254. The name means "long wood or clearing".

A Roman villa has been excavated just south of the village.

The manor was probably a possession of the Abbey of St. Albans, the records of which have been lost. Following the Norman Conquest of 1066 the manor was one of hundreds given to Robert, Count of Mortain, uterine half-brother of King William the Conqueror. His tenant was a certain Ralf. The present village developed as a linear village along the old road from London to Berkhamsted and beyond to the Midlands. In the Domesday Book of 1086, Langley was in the hundred of Danish. By 1346 the place was known as Kyngeslangley and by 1428 as Lengele Regis.

In about 1276 the manor was purchased by Queen Eleanor of Castile (1241-1290), wife of King Edward I, and Kings Langley Palace was built on the hill to the west of the village with a deer park extending to the south. King's Langley Priory, of the Dominican Order, of which remains survive, was founded next to the palace. The palace and the grand priory church fell into disrepair at the Dissolution of the Monasteries and little remains above ground level.

The Church of All Saints was built during the 14th century on the site of an earlier church.

It was the birth-place of Edmund of Langley, 1st Duke of York (1341-1402), 4th surviving son of King Edward III (grandson of Edward I), whose tomb survives in All Saints Church. The body of King Richard II, eldest grandson and successor of King Edward III, was buried here after his probable murder at Pontefract Castle in 1400. It was later removed to Westminster Abbey, next to the Palace of Westminster.

The 18th century Sparrows Herne turnpike road (later the A41 trunk road) traversed the Chilterns via the valley of the River Gade and ran down the village high street. The 16th century Saracen's Head public house is a coaching inn which flourished in this period.

The Grand Union Canal dating from 1797, and the 1838, London and Birmingham Railway which later became the West Coast Main Line, (the main railway line from London to the north west) pass just east of the village at Kings Langley railway station. There are many businesses located near the station in Home Park Industrial Estate which is also the site of the Construction and Engineering Centre of West Herts College.

20th century housing developments have led to the village spreading out on either side of the main road. The A41 has now been diverted west of the village leaving the high street to local traffic for the first time in centuries.

During the Second World War, the village was home to the secret headquarters in Britain of the Polish Underground army based at Barnes Lodge just off the Hempstead Road near Rucklers Lane.

Kings Langley was the site of the factory making Ovaltine chocolate drink; the listed factory facade, designed c.1923 by James Albert Bowden is now all that is left and still stands alongside the railway line among a new housing development. The Ovaltine factory itself has been converted into a series of flats and duplexes.

The former Ovaltine Egg Farm was converted into energy-efficient offices which house Renewable Energy Systems. The complex incorporates a highly visible 225 kW Vestas V29 wind turbine alongside the M25.

Kings Langley School is the local comprehensive school, situated on Love Lane to the west of the village.

Kings Langley was also the site of a Waldorf School, the Rudolf Steiner School Kings Langley which closed in 2019. This was built on the grounds of the old palace, of which only a small basement part of a pillar remains to be seen. There was a small display cabinet of finds from the palace period in the school entrance foyer.

The village became twinned with Achiet-le-Grand in France in November 2009, in honour of Christopher Cox from the village who won a Victoria Cross in fighting near Achiet-le-Grand in the First World War.