Member of the vertebrate class Amphibia, which generally spend their larval (tadpole) stage in fresh water, transferring to land at maturity (after metamorphosis) and generally returning to water to breed. Like fish and reptiles, they continue to grow throughout life, and cannot maintain a temperature greatly differing from that of their environment. The class contains 4,553 known species, 4,000 of which are frogs and toads, 390 salamanders, and 163 caecilians (wormlike in appearance).

The 1990s has seen a marked decline in amphibian populations worldwide from causes other than loss of habitat, notably infectious diseases. In 1998 an international summit on amphibian health was held at San Diego Zoo in an attempt to determine why infectious diseases are suddenly causing such high rates in mortality within amphibian populations.

One of the causes of death is a previously unknown parasitic fungus. The fungus, which is yet to be named, was discovered in 1998 independently by US and Australian researchers.