The genus Ansonia (stream toads) currently includes roughly three dozen recognized species distributed from Myanmar to Sundaland and the Philippines, and many more are likely to be discovered. Species of this genus have relatively long, slender limbs and narrow bodies. They are small to medium-sized toads, typically brownish in coloration, with dry, keratinized, warty skin that may bear small spines. Unlike many other bufonids, they lack distinct parotoid glands.

Ansonia species inhabit forest streams, and their tadpoles are rheophilous—adapted to life in flowing water. Tadpoles of different species show varying degrees of adaptation to current velocity. On Borneo, Ansonia tadpoles often occur alongside those of the ranid genus Meristogenys, sometimes sharing the same submerged or overflowed rocks. They are active both day and night, though they tend to be more exposed after dark, when they feed on the surfaces of current-washed rocks.

The taxonomy of Ansonia remains in flux, and further revisions are expected. Some species are difficult to identify, and as a result, the true diversity of the genus is still not fully understood.