Tongerlo Abbey is a Premonstratensian monastery at Tongerlo (A.K.A. Tongerloo) in Westerlo near Antwerp, Belgium.
It was founded in 1128 in honour of the Blessed Virgin Mary, by Giselbert of Kasterlee, who not only gave the land, but also himself became a lay brother in the new community. The first monks were sent from St. Michael's Abbey, Antwerp, under Henry, who had come with Saint Norbert, founder of the Premonstratensian Order, to Antwerp to extirpate the Tanchelmite heresies. The charter of its foundation was signed, amongst others, by Bernard of Clairvaux and by Waltman, first abbot of Antwerp. The Bishop of Cambrai granted synodal rights to the abbots.
From small beginnings the abbey became influential in the district called Campine, now in north-east Belgium and the south of the Netherlands, then a wild area. The bishops of Cambrai, the chapters of Liège and Maastricht, and several landowners entrusted the charge of parishes, with the right of patronage, to the abbey. In time the abbey had to provide priests for some forty parishes in these parts.
With the erection of new dioceses (1559–60) in Belgium and the Netherlands, heavy burdens were cast on the abbey, for not only had it to provide funds for the new diocese of 's-Hertogenbosch, but the new bishop was put at its head as abbot. This state of affairs lasted until 1590, when, to obtain its independence, the abbey had to give up much property in support of the new diocese. The abbey was a centre of education. It possessed one of the largest libraries, and was able to take up the work of the Bollandists.