Holyrood Abbey is a ruined abbey of the Canons Regular in Edinburgh, Scotland. The abbey was founded in 1128 by David I of Scotland. During the 15th century, the abbey guesthouse was developed into a royal residence, and after the Scottish Reformation the Palace of Holyroodhouse was expanded further. The abbey church was used as a parish church until the 17th century, and has been ruined since the 18th century. The remaining walls of the abbey lie adjacent to the palace, at the eastern end of Edinburgh's Royal Mile. The site of the abbey is protected as a scheduled monument.

Rood is a word for the cross on which Jesus Christ was crucified; thus the name Holyrood is equivalent to "Holy Cross".

Legend relates that in 1127, while King David I was hunting in the forests to the east of Edinburgh during the Feast of the Cross, he was thrown from his horse after it had been startled by a hart. According to variations of the story, the king was saved from being gored by the charging animal when it was startled either by the miraculous appearance of a holy cross descending from the skies, or by sunlight reflected from a crucifix which suddenly appeared between the hart's antlers while the king attempted to grasp them in self-defence. As an act of thanksgiving for his escape, David I founded Holyrood Abbey on the site in 1128.

In the church was preserved, in a golden reliquary, an object said to be a fragment of the True Cross brought by David's mother, St. Margaret, from Waltham Abbey, and known thereafter as the Black Rood of Scotland (the Holyrood (cross)). At the battle of Neville's Cross, in 1346, this precious relic fell into the hands of the English, and it was placed in Durham Cathedral, from where it disappeared at the Reformation.

The abbey was originally served by a community of Augustinian Canons Regular from Merton Priory. The layout of the original church at Holyrood, now known only from excavations, probably came from the 1125 church at the priory. In 1177 the papal legate Vivian held council here. In 1189 the nobles and prelates of Scotland met here to discuss raising a ransom for William the Lion.

The original abbey church of Holyrood was largely reconstructed between 1195 and 1230. The completed building consisted of a six-bay aisled choir, three-bay transepts with a central tower above, and an eight-bay aisled nave with twin towers at its west front. Some scholars believe the high vaults to be sexpartite (though this is not clearly supported by the 17th century illustrations of the interior). Such a design was probably archaic in that period, and difficult to execute or maintain. Evidence of the construction qualities of the stonemasons has remained on the S aisle vaults, which are set on an almost square plan of 4.4 m (14 feet), but built relatively roughly, with thin flagstones and not much attention to keeping the vertices straight. They were probably plastered, with exposed thin ribs.

Among the chief benefactors of Holyrood during the four centuries of its existence as a religious house were Kings David I and II; Robert, Bishop of St. Andrews; and Fergus of Galloway.

Around the abbey was a five-mile area of sanctuary, taking in much of Holyrood Park, where debtors and those accused of crimes could appeal to the Bailie of Holyroodhouse for protection. Brass sanctuary stones mark the boundary of the sanctuary on the Royal Mile. Those granted sanctuary would be given lodgings in the buildings around the abbey and obtained the nickname 'Abbey Lairds'.