structural:expansion, information:extraction
Reproduction and parenting

Crocodilians are generally polygynous, and individual males try to mate with as many females as they can. Monogamous pairings have been recorded in American alligators, and parthenogenesis has been observed in the American crocodile. Dominant male crocodilians patrol and defend territories which contain several females. Males of some species, like the American alligator, try to attract females with elaborate courtship displays. During courtship, crocodilian males and females may rub against each other, circle around, and perform swimming displays. Copulation typically occurs in the water. When a female is ready to mate, she arches her back while her head and tail dip underwater. The male rubs across the female's neck and then grasps her with his hindlimbs, placing his tail underneath hers so their cloacas align and his penis can be inserted. Intermission can last up to 15 minutes, during which time the pair continuously submerge and surface. While dominant males usually monopolise females, single American alligator clutches can be sired by three different males.

Depending on the species, female crocodilians may construct either holes or mounds as nests, the latter made from vegetation, litter, sand, or soil. Nests are typically found near dens or caves. Those made by different females are sometimes close to each other, particularly in hole-nesting species. The number of eggs laid in a single clutch ranges from ten to fifty. Crocodilian eggs are protected by hard shells made of calcium carbonate. The incubation period is two to three months. The sex of the developing, incubating young is temperature dependant. Constant nest temperatures above 32 °C (90 °F) produce more males, while those below 31 °C (88 °F) produce more females. However, sex in crocodilians may be established in a short period of time, and nests are subject to changes in temperature. Most natural nests produce hatchlings of both sexes, though single-sex clutches do occur.

The young may all hatch in a single night. Crocodilians are unusual among reptiles in the amount of parental care provided after the young hatch. The mother helps excavate hatchlings from the nest and carries them to water in her mouth. Newly hatched crocodilians gather together and follow their mother. Both male and female adult crocodilians will respond to vocalizations by hatchlings. For spectacled caimans in the Venezuelan llanos, individual mothers are known to leave their young in the same nurseries, or crèches, and one of the mothers guards them. Hatchlings of many species tend to bask in a group during the day and disperse at nightfall to feed. The time it takes young crocodilians to reach independence can vary. For American alligators, groups of young associate with adults for one to two years, while juvenile saltwater and Nile crocodiles become independent in a few months.