Frog is a small, tailless animal with bulging eyes. Almost all frogs also have long back legs. The strong hind legs enable a frog to leap distances far greater than the length of its body. Frogs live on every continent except Antarctica, but tropical regions have the greatest number of species. Frogs are classified as amphibians. Most amphibians, including most frogs, spend part of their life as a water animal and part as a land animal. Frogs are related to toads but differ from them in several ways.

The first frogs appeared on Earth during the Jurassic Period, which lasted from about 213 million years ago to about 145 million years ago. Thousands of species of frogs and toads have developed from these early ancestors. Some species spend their entire life in or near water. Others live mainly on land and come to the water only to mate. Still other species never enter the water, not even to mate. Many kinds are climbers that dwell in trees. Others are burrowers that live underground.

Throughout history, frogs have been the source of superstitions. One old myth says that frogs fall from the sky during a rain. Actually, many species that live underground leave their burrows during or after a rain at the start of the mating season. Because people seldom see these frogs the rest of the year, they imagine the animals fell from the sky with the rain.