Most salamanders are relatively small for vertebrates, usually less than 15 cm long, although the aquatic cryptobranchid salamanders of the genus Andrias may exceed 1.5 m in length. Salamanders inhabit nearly all northern temperate regions of the world where moist and cool habitats occur. The greatest phylogenetic diversity of salamanders is in North America where representatives of 9 of the 10 extant taxonomic families occur. Lungless salamanders of the family Plethodontidae occur also in tropical areas of Central and South America. Terrestrial salamanders are usually found on the forest floor under rocks or logs, from which they emerge at night to feed.
Aquatic forms live on the bottoms of streams or ponds, often under stones.
Salamanders are usually seasonal in their activity and are easily found only during their active season, which differs among species. In addition to presence of a tail and usually two pairs of limbs of approximately equal size, salamanders are distinguished from other amphibians by a combination of several technical features of the skeleton and musculature. Some extinct species known only from fossils are grouped into the families Batrachosauroididae, Karauridae, Prosirenidae and Scapherpetontidae. Each extant family of salamanders is described in more detail on further pages. Within the Salamandroidea, the Amphiumidae, Rhyacotritonidae and Plethodontidae each represent ancient phylogenetic divergences and have no close extant relatives.