Vallbona Abbey, otherwise the Monastery of Santa Maria de Vallbona (Catalan: Santa Maria de Vallbona de les Monges; Spanish: El Real Monasterio de Santa María de Vallbona), is a Cistercian nunnery in Vallbona de les Monges, in the comarca of Urgell, Catalonia, Spain. Founded in the early 12th century, and built between then and the 14th century, it is one of the most important monastic sites in Catalonia. Its church represents an example of transition between Romanesque and Gothic architecture. The abbey was declared a national monument on 3 June 1931.

Together with the monasteries of Poblet and of Santes Creus it forms part of the Cistercian Route.

Initially the monastery consisted of a community of hermits or anchorites of both sexes, founded by Ramon de Vallbona and documented from 1157, which followed the Rule of St. Benedict. In 1163 the community received a gift of land from Ramon Berenguer IV, count of Barcelona. By 1175 only a small group of nuns remained, who decided to affiliate themselves to the Cistercian Order. The first abbess, Oria Ramirez, was appointed in the following year from Tulebras Abbey (Monastery of Santa Maria de la Caridad) in Tulebras, Navarre.

The abbey received several privileges from King Alfonso II of Aragon and his wife Sancha of Castile, and was subsequently able to expand thanks to the numerous gifts from noble families. From Pope Innocent III the abbey received in 1198 and 1200 the grant of Papal immunity and protection of goods, and a bull in 1201 regulated the enclosure and ensured its independence from the episcopate. King James I of Aragon not only stayed in the abbey on repeated occasions but also sponsored its construction.

Thanks to the numerous properties received through donations and wills, among them that of Count Ermengol VII himself, the sizeable lordship of the abbey was formed between the 12th and 14th centuries, especially in the County of Urgel. Legal confirmation was achieved under the mandate of Abbess Saurena de Anglesola (1379-1392), who bought from King Peter III of Aragon the civil and criminal jurisdiction of all the monastery's possessions for 22,000 Barcelona salaries. These acquisitions allowed the establishment of the barony of Vallbona and made the monastery the centre of political and legal life for all the towns and districts that made it up. At this time, the community was made up of about 150 nuns, most of whom belonged to the Catalan nobility, from families such as the Cardonas, Cerveras, Queralts, Boixadors and Anglesolas.

The abbey's library together with the scriptorium achieved great fame. Fourteen codices from the 13th century were copied and illustrated by the old nuns and are kept in the archive with numerous old documents of great interest for regional and national historiography. The pharmacy, which supplied all the villages of the barony, has surviving documentation from the 15th century.

The abbey was deeply impacted by the Catalan civil war of 1462-1472 and later the Council of Trent (1545-1563), which had a notable repercussion on the abbey: one of its agreements prohibited the existence of female religious communities in unpopulated places, which forced the nuns in 1573 to cede part of their lands to people from other places, mainly Montesquieu, in order to create a centre of population around the abbey so that it could stay where it was. This was the origin of the present town of Vallbona de las Monjas.

For this purpose, all the monastery's external buildings were converted (similar to those that still remain in Poblet Abbey and Santes Creus), and only the strictly conventual premises were retained, apart from the church and the cloister. The following times were difficult. In the 17th century there were disputes with the Cistercian order, mainly with Poblet Abbey over the dues Vallbona had to pay them. These weakened the abbey's economy, and the financial situation was made still worse by the ravages caused by the Reapers' War (1640-1652), followed by the War of the Spanish Succession (1705-1717) and the Roussillon War (1788-1795). The nuns also had numerous disputes with the towns belonging to their barony. The Ecclesiastical confiscations of Mendizábal in the 1830s caused them to be exclaustrated for six months, but they were able to continue monastic life and did not suffer as much damage as the monasteries of Poblet or Santes Creus.