Jarrah Forest is an interim Australian bioregion and ecoregion located in the south west of Western Australia. The name of the bioregion refers to the region's dominant plant community, jarrah forest – a tall open and open forest in which jarrah (Eucalyptus marginata) is the dominant overstorey species.

Jarrah Forest is recognised globally as a significant hotspot of plant biodiversity and endemism, and is also managed for land uses such as water, timber and mineral production, recreation, and conservation.

The bioregion stands on the 300-metre-high (980 ft) Yilgarn block inland plateau and includes wooded valleys such as those of Western Australia's Murray River and the Helena River. The Darling Scarp forms the western edge of the plateau, and the Swan Coastal Plain lies between the scarp and the coast. The scarp generally forms the western boundary of the bioregion, although it extends to the west coast at Cape Naturaliste. At the southern end of the plateau is the Whicher Range and inland is the lower Blackwood Plateau. The south eastern interior of the region includes the peaks of the Stirling Range, now preserved within Stirling Range National Park.

Soils in the jarrah forest are infertile, especially for phosphorus, and are often salt-laden.

The bioregion covers an area of 4,509,074 hectares (11,142,160 acres). It is divided into two sub-regions: Northern Jarrah Forest comprising 1,898,799 hectares (4,692,030 acres), and Southern Jarrah Forest comprising 2,610,275 hectares (6,450,130 acres).

The Swan Coastal Plain bioregion lies to the west below the scarp. The Warren bioregion, also known as the Jarrah-Karri forest and shrublands, is to the south. The Avon Wheatbelt bioregion, part of the Southwest Australia savanna ecoregion, is to the east.

The area has a warm Mediterranean climate, with more annual rainfall – 1,300 millimetres (51 in) – on the scarp than inland or to the north-east – 700 millimetres (28 in).

Jarrah Forest is unique in that it shares the co-dominate Corymbia species marri (Corymbia calophylla). Marri, formerly formally known as Eucalyptus calophylla, is a prevalent canopy species and the jarrah forest is commonly called jarrah-marri forest. Other eucalypts are present but in much less abundance. The Southern Jarrah Forest contains extensive areas of wetland vegetation in the south–east, dominated by paperbarks including the swamp paperbark (Melaleuca rhaphiophylla), and other eucalypts such as the swamp yate (Eucalyptus occidentalis) and the Albany blackbutt (Eucalyptus staeri).