Hatfield Broad Oak (also known as HBO or Hatfield Regis) is a village and civil parish in the Uttlesford district of Essex, England, about five and a half miles south-east of Bishop's Stortford. Near the church of St Mary the Virgin is former Benedictine priory Hatfield Regis Priory.
At around the parish is one of the largest in Essex, stretching four miles (6 km) north of the village, and was formerly divided into four "quarters": Town Quarter, Woodrow Quarter, Heath Quarter, and Broomsend Quarter. At the north end of the parish lies Hatfield Forest, known for its large oak trees.
The name Hatfield Broad Oak has been used since at least 1136, and the eponymous oak was mentioned in record in 1295. The forest still contains the fenced remains of a very large oak known as the "Doodle Oak", estimated as 850 years old, though it is believed to be a different tree to that which gave the parish its name. Hatfield forest is now in the possession of the National Trust.
Hatfield was at one time a thriving market town. At the time of the 2001 census it had a population of 1,600.