Rhododendron (from Ancient Greek ῥόδον rhódon "rose" and δένδρον déndron "tree") is a genus of over 1 000 species of woody plants in the heath family, either evergreen or deciduous. Most species have showy flowers.

Azaleas are two subgenera of Rhododendron. The flowers of some hydrangeas can appear similar to those of some rhododendrons, but Hydrangea is in a different order.

The rhododendron is the national flower of Nepal.

Rhododendron is a genus characterized by shrubs and small to (rarely) large trees, the smallest species growing to 10–100 centimetres (3.9–39 in) tall, and the largest, R. giganteum, reported to over 30 metres (98 ft) tall. The leaves are spirally arranged; leaf size can range from 1–2 cm (0.39–0.79 in) to over 50 cm (20 in), exceptionally 100 cm (39 in) in R. sinogrande. They may be either evergreen or deciduous. In some species the underside of the leaves is covered with scales (lepidote) or hairs (indumentum). Some of the best known species are noted for their many clusters of large flowers. There are alpine species with small flowers and small leaves, and tropical species such as section Vireya that often grow as epiphytes. Species in this genus may be part of the heath complex in oak-heath forests in eastern North America.