Ironbark is a common name of a number of species in three taxonomic groups within the genus Eucalyptus that have dark, deeply furrowed bark.

Instead of being shed annually as in many of the other species of Eucalyptus, the dead bark accumulates on the trees, forming the fissures. It becomes rough after drying out and becomes impregnated with kino (red gum), a dark red tree sap exuded by the tree. The tree is so named for the apparent resemblance of its bark to iron slag. The bark is resistant to fire and heat and protects the living tissue within the trunk and branches from fire. In cases of extreme fire, where leaves and shoots are removed, the protective bark aids in protecting epicormic buds which allow the tree to reshoot.

Being a very dense, hard wood, a length of ironbark is often used as a bug shoe on the bottom of a ship's skeg to protect it from shipworms. Ironbark was widely used in the piles of 19th and early 20th century bridges and wharves in New Zealand.