The American Bullfrog (Rana catesbeiana) is an aquatic frog, a member of the family Ranidae, or "true frogs", native to much of North America. This is a frog of larger, permanent water bodies, swamps, ponds, lakes, where it is usually found along the water's edge . On rainy nights, bullfrogs along with many other amphibians, go overland and may be seen in numbers on country roads.

American Bullfrogs live longer in warm weather. They have been widely introduced across North America (see range map). The original, naturally determined range did not include far western regions where it is found today.

 
Bullfrogs grow on average to be about 3 and a half to 6 inches (9-15 cm) long in bodylength (although there are records of some as big as 8 inches), legs add another 7-10 inches (17 - 25 cm) to length. Adult bullfrog skeleton is representative of tetrapod vertebrates, comprising an axial skeleton (skull and vertebrae) and an appendicular skeleton (pectoral girdle and forelimbs, pelvic girdle and hindlimbs). Ranids, however, lack ribs. The pronounced pair of dorsal humps in the back of ranid frogs are the ends of the pelvic ilia, homologues of the human hips.

The bullfrog skull is highly fenestrated. The orbits open ventrally through the roof of the mouth to accommodate eye retraction during locomotion and swallowing. The skull bears a continuous row of tiny teeth on the maxilla and premaxilla and a pair of small vomerine teeth on the palate. The mandible is toothless.

The bullfrog nervous system consists of a brain, spinal cord, and peripheral nerves including cranial nerves, spinal nerves, and sympathetic nerves serving organs such as the heart, gastrointestinal tract, kidneys, gonads.

Females have an eardrum (tympanum) the same size as their eye. Males eardrums are larger.