Most Mimosa species are herbs or undershrubs; some are woody climbers; and a few are trees. They are often prickly. The leaves of most are bipinnate (i.e., the leaflets of the feather-formed leaves, in turn, bear leaflets). The roots of some species are poisonous; others contain substances irritating to the skin. Mimosas are characterized by small regular flowers with valvate corolla.

Mimosas are widely cultivated partly for the beauty of their bipinnate foliage and partly for their interesting response to light and mechanical stimuli. A few species have leaves that are sensitive to light and touch; they droop in response to darkness and close up their leaflets when touched. When shaken in any way, the leaves close and droop simultaneously. The well-known sensitive plant, or humble plant (M. pudica), native to Central America, and similar species such as M. sensitiva are commonly grown in greenhouses.

Many species of the related genus acacia are commonly but erroneously called mimosas.