Tilia is a genus of about 30 species of trees or bushes, native throughout most of the temperate Northern Hemisphere. The tree is known as linden for the European species, and basswood for North American species. In Britain and Ireland they are commonly called lime trees, although they are not related to the citrus lime. The genus occurs in Europe and eastern North America, but the greatest species diversity is found in Asia. In Chinese, "椴/duàn" or "椴樹/duànshù" is a general term for Tilia species. Under the Cronquist classification system, this genus was placed in the family Tiliaceae, but genetic research summarised by the Angiosperm Phylogeny Group has resulted in the incorporation of this genus, and of most of the previous family, into the Malvaceae.

Tilia species are mostly large, deciduous trees, reaching typically 20 to 40 m (65 to 130 ft) tall, with oblique-cordate (heart-shaped) leaves 6 to 20 cm (2+1⁄4 to 7+3⁄4 in) across. As with elms, the exact number of species is uncertain, as many of the species can hybridise readily, both in the wild and in cultivation. They are hermaphroditic, having perfect flowers with both male and female parts, pollinated by insects.

Tilia is the only known ectomycorrhizal genus in the family Malvaceae. Studies of ectomycorrhizal relations of Tilia species indicate a wide range of fungal symbionts and a preference toward Ascomycota fungal partners.