Shrubs or trees, with opposite leaves and no stipules. The flowers are in clusters and usually perfect, but sometimes those at the margins of the clusters are without pistils or stamens and larger than those in the middle; the calyx usually with four to ten sepals, and in sterile flowers often conspicuously enlarged; the petals four to ten; the stamens eight to many; the ovary wholly or partly inferior; the styles separate or united, sometimes lacking; the fruit a capsule. Many very ornamental garden shrubs, such as Deutzia and Hydrangea, are included in this family.

There are several kinds of Fendlera, natives of North America; shrubs, with white or pink flowers, with four sepals and four petals, the latter with claws. The eight stamens have two-forked filaments and the ovary is partly inferior, with four styles.