Æbelholt Abbey (Danish: Æbelholt Kloster) was an Augustinian monastery situated in Tjæreby, 5 km west from Hillerød in Region Hovedstaden, Denmark.
The monastery was first established on Eskilsø Island in Roskilde Fjord in 1104. While no remains of the wooden abbey have survived, the stone abbey church there still remains, though in ruins. It was 24 meters long and had a nave, choir, and apse in the Romanesque style. The monks became "unruly" and Bishop Absalon of Roskilde, determined to obtain a new Augustinian superior, sent for his friend, William, abbot of the abbey of Sainte-Geneviève in Paris. When William arrived in 1165 with three French canons there were only six religious left at Eskilsø, two of whom were dismissed when they refused to submit to the new rule.
In 1167 the abbey moved to Æbelholt in Tjæreby, supported by a donation of land from Absalon in Tjæreby Parish and endowed with several income-producing farms, tithes from many north Zealand churches, and several mills. The monastery on Eskilsø was closed. The first church and abbey at Æbelholt were made of timber. Construction began almost immediately on a new abbey church of limestone which was completed in 1210.
Abbot William experienced considerable initial difficulties. The three French canons returned to Paris, finding conditions in Denmark too bleak. A few of the Danish canons plotted to murder him when he ordered that they eat "herbs and leaves" instead of their usual meals. The "Life of St. William" notes some of the ways in which they considered killing him, either by setting fire to a pile of straw near his bed in the dormitory, putting him in a sack and drowning him, or taking an axe to him. Eventually William's piety, fairness, wisdom, and intelligence won them and the local populace over. He was considered a saint in his own lifetime. He was highly regarded by several kings of Denmark and served as an intermediary between the pope and the Danish monarchy.