The genus Ansonia (Stream Toads) currently includes about three dozens of recognised species distributed from Myanmar to Sundaland and the Phillippines, many more are expected to be discovered. Species of this genus have relatively long and slender appendages and slender bodies. These toads are small to medium in size. Most species have a brownish coloration and dry, keratinized, warty skin, sometimes with small spines on warts. They lack a distinct parotoid gland.

These toads are found along streams. Their tadpoles are rheophilous, i.e., adapted to living in flowing waters. The tadpoles of different species show a variable degree of adaptation to velocity of currents. On the island of Borneo, they are often encountered with tadpoles of the ranid genus Meristogenys on the same rocks in the streams. Tadpoles are active day and night, but are more exposed during the night when they feed on top of overflown rocks in the current.

The taxonomy of this genus ist still in a state of flux. Taxonomic changes can be expected over time. Some species are not easy to identify. As a result the true diversity of Ansonia is still unknown.