The Illyrian deciduous forests is a terrestrial ecoregion in southern Europe, which extends along the eastern coast of the Adriatic Sea.

The Illyrian deciduous forests stretch along the eastern coast of the Ionian and Adriatic Seas, and occupies 40,600 km2 (15,700 sq mi) in Northern Greece, Albania, Montenegro, Bosnia and Herzegovina, Croatia, Slovenia and Northern Italy around Trieste.

The climate of the ecoregion is mostly of Köppen's Mediterranean type with hot summers (Csa) to humid subtropical with wet winters (Cfa).

Due to the wide altitudinal range of this ecoregion the highest elevations (above 1,000 m (3,300 ft)) are covered with conifer forests, with a mixed broadleaf vegetation and maquis shrubland occurring lower.

Evergreen trees and maquis shrubs Quercus ilex, Quercus coccifera, Pinus halepensis, Pinus pinea, Pistacia terebinthus, P. lentiscus, Erica arborea, Juniperus oxycedrus, J. macrocarpa, Olea europaea, Arbutus unedo, A. andrachne, Nerium oleander become predominant near the coast.