The members of this order are characterized by lizard-shaped bodes with a type of armored skin. The entire of bodies of these animals are covered in large, strong and partially ossified horny plates. This order has changed very little over the last 65 million years.

All crocodilians are carnivorous. During the first year of life they live on small animals such as frogs, insects, mollusks and crustaceans. As they grow, their diet increases to larger mammals, birds and fish. They will eat almost anything they can overpower. Feeding takes place in the water, but not underwater. Cannibalism often occurs among the crocodilians. For this reason, after separation from their mothers, the young never live in the same area as adults.

Crocodilians have eyes and nostrils set high on their heads, enabling them to see and breathe while floating in rivers, streams and lakes. A third eyelid allows them to maintain acute vision when submerged. Their ears are protected by a scaly flap and allows for excellent hearing when out of the water. Both nostrils and ears close automatically when underwater. A false palate in the back of the throat closes the glottis when submerged. This allows them to feed or drown their prey without drowning themselves.

Their brain and heart are more advanced than other reptiles. The ventricles of the heart are completely divided, and allows more oxygenated blood to enter the brain. They have a true cerebral cortex, which permits for more learned behavior, as opposed to instinctive reactions. Conical teeth in their long snouts are angled horizontally and vertically into the jaw. Teeth are replaced throughout life. Replacement is quick since each tooth contains a small replacement tooth within the pulp cavity.

The forelegs end in fingers separated down to the base. The hind legs have five toes connected by webbing. This aids them in swimming efficiently using serpentine movements of the body or strokes of the tail. The tail is also used as a formidable weapon. Locomotion on land consists of three different gaits; walking, galloping and tobogganing, used for quick retreat into the water by sliding the belly and using the legs as paddles.

Crocodilians spend most of the day basking in the sun to raise body temperature. Gaping jaws are a means of cooling themselves by evaporation of water through the lining of the mouth. Territorial disputes arise occasionally during breeding season. In all species, the males are larger than the females and always court the females. During copulation, which takes place in the water, the pair sinks to the bottom. Around 2 months later, the female lays her clutch, ranging from 15 to 100 hard calcified eggs. The females display strong maternal instincts from the time the eggs are laid and stay close to the nest for the entire incubation period. Even after the hatchlings are born, the mother may attend to them for over a year.