Grestain Abbey (or Grestein Abbey, French: Abbaye Notre-Dame de Grestain) was an 11th-Century Benedictine monastery near the town of Fatouville-Grestain, which is located in the modern-day Eure département of Upper Normandy, France.

[1] Many churches mentioned in the Domesday Book of 1086 cite Grestain as the founding establishment.

The Abbey was founded in 1050 by Herluin de Conteville and his wife Arlette, mother of William the Conqueror.

[4] Herluin's son, Robert de Mortain, half-brother of William, was the principal benefactor, endowing it with his revenues from England.

The church buildings were demolished around 1766 and the rest of abbey destroyed in 1790; of these buildings, only a few ruins remain, integrated into the Château de La Pommeraye (a private property): a defensive wall, a 13th-Century portal, an 18th-Century manor with a 13th-Century floor, and remains of the church.