Paimpont Forest (French: Forêt de Paimpont, Breton: Koad Pempont), also known as Brocéliande Forest (French: Forêt de Brocéliande), is a temperate forest located around the village of Paimpont in the department of Ille-et-Vilaine in Brittany, France. Covering an area of 9,000 hectares, it is part of a larger forest area that covers the neighboring departments of Morbihan and Côtes-d'Armor. It contains the castles Château de Comper and Château de Trécesson as well as the Forges of Paimpont, a national historical site. It has been associated with the forest of Brocéliande and many locations from Arthurian legend, including the Val sans retour, the tomb of Merlin, and the fountain of Barenton.

The forest is located in the northwestern French region of Brittany, about 30 km southwest of the city of Rennes. It occupies mainly the territory of the commune of Paimpont but extends to bordering communes in the departments of Ille-et-Vilaine and Morbihan, mainly Guer and Beignon in the south, Saint-Péran in the northeast, and Concoret in the north.

The woodland surrounding Paimpont is the remains of a denser and much larger forest. It is mainly a broadleaved forest, mostly oaks and beech, with areas of conifers either inside after clear-felling or on the periphery as a transition to moorland, for example towards the west in the area of Tréhorenteuc and the Val sans retour. The relative altitude of the forested massif helps produce a climate close to the oceanic climate of the Finistère coast. This, in addition to west and southwest winds that carry clouds and rain, supports ample vegetation. The surplus of water feeds the many brooks at the bottoms of small valleys before flowing into the river Aff, then into the Vilaine, and on to the area around Redon in the south of Ille-et-Vilaine.

The road from Forges to Concoret, which goes north through Paimpont, separates the western "high forest" (haute forêt) and the eastern "low forest", both of comparable size. In the high forest, the altitude decreases regularly from the highest point to 258 m, regularly offering views southwest towards the department of Morbihan; similarly, to the north are views towards the commune of Mauron on the edge of Côtes-d'Armor.

Paimpont Forest was known as Brocélien in the 15th century. In Breton, it was called Brec'Helean. It has been repeatedly logged for construction needs of the city of Rennes, in particular in the 15th century. Because of its importance, the forest was put under royal jurisdiction.

The Forges of Paimpont were the most important wood-fueled forges of Brittany, operating from the 16th century until the end of the 19th century. Their location was enabled by the proximity of an open-cast deposit of iron ore at Gelée (a site near the village of Paimpont), the existence of a major river system, and the easy supply of locally produced charcoal. The forest was overexploited for the needs of the forges.

During the French Revolution, the abolition of protection triggered massive clear-cutting of the forest as the wood was excessively exploited to power the blast furnaces of local industry, which employed charcoal. In 1804, the prefect of the department wrote that the forest at Paimpont was in a state of degradation and threatened by complete destruction.

In 1875, the forest was bought from Prince Philippe, Count of Paris by shipowner and industrialist Louis Levesque, for rest and pleasure. The new owner created the Domaine de Paimpont and organized hunts of wild boars and deer. Exploitation of the forest by the local population was limited to be only under licenses and the supervision of private forest rangers.