Forest Abbey, 12th-century Benedictine abbey complex in Forest district, Belgium

Forest Abbey is a monastic complex that originated in the 12th century and stands in the Forest district of Brussels. The compound features classical architecture with an entrance porch, outbuildings arranged in a semicircular pattern, and two residential buildings constructed in neoclassical style.

Forest Abbey began as a Benedictine priory for women, established in 1105 when the Bishop of Cambrai gave the parish church to Affligem Abbey. It became an independent abbey in 1239, with Pétronille de Gand as first abbess. A fire destroyed much of the complex on 26 March 1764, and the abbey was suppressed on 8 October 1796 and sold the following year.

The abbey church long housed relics of Saint Alena alongside the parish church; since 1796 they have been kept only in the parish church of Saint-Denis. The 18th-century outbuildings now belong to the municipality and host seminars, banquets and exhibitions.

The 18th-century outbuildings stand beside the Church of St Denis, on the north side of the former abbey grounds, since the Sainte-Alène chapel blocked expansion to the south. The buildings are owned by the municipality of Forest and used for seminars, banquets and exhibitions, so access follows the cultural centre's programme rather than fixed visiting hours.

The monastery remained under continuous female leadership for more than seven centuries, an exceptional achievement for religious communities of that era. This extended tradition of women in leadership positions set it apart as a rare example during medieval and early modern times.