The name of amphibians is derived from the Greek word for double life, which reflects their capability to utilize both terrestrial and aquatic habitats. However, not all amphibians can switch between environments. Some species are purely tenants of the land, while others only live in the water.

The three living orders of amphibians, Anura, Caudata, and Apoda, contain species that vary greatly in appearance. However, certain characteristics are shared by all, uniting them in a single class, Amphibia. The most defining common feature is that they are the only tetrapods that lay anamniotic eggs, which require moisture and do not have shells. Amphibians also have a three-chambered heart, two lungs, and a glandular skin that lacks any epidermal structures, such as hair or scales.

Frogs and other amphibians are often used as indicator species. Their skin is very permeable and they absorb and concentrate toxins in their fatty tissues. Also, amphibians are particularly sensitive to pollution because they live at the threshold of two different habitats. When there are lots of healthy frogs in an area, scientists know that the ecosystem is also relatively healthy. However, when populations suddenly dissipate, die off, or when there is an increase in mutations, something has clearly changed for the worse in their environment.