Older classifications such as the Cronquist system placed the Violaceae in an order named after it, the Violales. However, more recent classifications such as that of the Angiosperm Phylogeny Group locate it in the Malpighiales.
Though the best-known genus, Viola, is herbaceous, most species are shrubs or small trees. The simple leaves are alternate or opposite, often with leafy stipules or the stipules are reduced in size. Some species have palmate or deeply dissected leaves. Many species are acaulescent. Inflorescences have solitary flowers or are paniculate; some species have cleistogamous flowers produced after or before the production of typically petaled flowers. Flowers are bisexual or unisexual (e.g. Melicytus), typically zygomorphic or actinomorphic with a calyx of five sepals that are persistent after flowering. Corollae have five mostly unequal petals, and the anterior petal is larger and often spurred. Plants have five stamens with the abaxial stamen often spurred at the base. The gynoecium is a compound pistil of three united carpels with one locule. Styles are simple, with the ovary superior, and many ovules. The fruits are capsules split by way of three seams. Seeds have endosperm.