The alligator snapping turtle's defining characteristics are its large head, strong jaws and hooked beak. It has a spiked, dark-brown carapace. Alligator snapping turtles have long, narrow tongues equipped with an appendage that looks like a worm to attract prey. Algae growing on these turtles' backs lends camouflage among the muddy river beds they inhabit.

Males can weigh up to 90 kilograms (200 pounds) with a carapace length of up to 80 centimeters (31 inches). 

Alligator snapping turtles are native to the southern United States. They are found in rivers and streams that feed into the Gulf of Mexico. Their range stretches from Iowa, west into Texas, and east into Georgia and northern Florida.  Genetic analyses revealed that there are three genetically distinct subpopulations of alligator snapping turtles, residing in the greater Mississippi River watershed, the Gulf coastal rivers east of the Mississippi River and the Suwannee River drainage system in Florida.

Alligator snapping turtles are predominantly aquatic, spending most of their time in the water. They can stay submerged for 40 to 50 minutes before needing to surface for air. They are only found in freshwater systems and tend to prefer the deeper beds of large rivers, canals and lakes. However, juveniles may be found in smaller streams.

Alligator snapping turtles are primarily carnivorous. They eat fish and other aquatic animals, but have also been known to eat small mammals and some vegetation. These turtles are most active at night and will scavenge or hunt for food. When hunting, these ambush predators stay motionless in the water and reveal the worm-like appendage on their tongues to lure unsuspecting prey.

Alligator snapping turtles reach sexual maturity between 11 and 13 years. They tend to mate in early spring. Because they are typically solitary, they may have to travel to find a mate. The male mounts the back of the female and holds her shell with all four feet during copulation. Females then travel inland to dig nests in the sand. They generally lay only one clutch per year, or possibly one every other year. Clutch sizes range from 10 to 60, and the eggs incubate for about 100 days.

This species was assessed in 1996 by the IUCN Red List and is listed as vulnerable. It is also protected under a listing in the CITES Appendix III. In the United States, protections for the alligator snapping turtle vary from state to state, ranging from prohibitions on collecting wild individuals for commercial use and personal use to restrictions on commercial use. It is illegal to capture wild alligator snapping turtles in Arkansas, Florida, Georgia, Indiana, Missouri and Tennessee, and a permit is required in Alabama, Illinois, Kansas, Louisiana, Oklahoma and Texas.

The largest threat facing alligator snapping turtles has been uncontrolled wild harvesting for their meat, unique shells and to sell as exotic pets. Because they are large and easy to capture, the turtles' meat is harvested for consumption in domestic and international markets. It was most popular in the 1970s and 1980s for use in canned soup.

There are three, genetically distinct subpopulations of alligator snapping turtles. Taking individuals from one or more of these populations could lead to local extirpation, which reduces the overall genetic variability that protects populations from disease outbreaks. Losing that genetic diversity would also make it more difficult to find founders for populations in breeding programs designed for species conservation. Consumers making informed, responsible choices about exotic meats and agricultural products can lessen the pressure on these animals.

Agriculture in areas that formerly hosted bottomland hardwood forest and streams also impacts alligator snapping turtles. The conversion of these lands into agricultural fields and commercial developments replaces suitable habitat. Riverside developments usurp the turtles by removing nesting sites. Activities in these areas lead to the degradation of aquatic habitats downstream, because agrochemicals, pesticides, silts and other dissolved solids reach the water and are carried downstream. These added inputs alter the pH, turbidity and flow of water in sites well beyond the reaches of human settlements.

Programs in Arkansas and the Lower Mississippi Valley that establish and protect waterfowl habitat have countered some of these impacts by maintaining suitable habitat for other freshwater species like the alligator snapping turtle. These protections, in turn, help maintain the overall health of that ecosystem.

Alligator snapping turtles are apex predators and, because of their position at the top of the food web, play an important role in the ecosystems they inhabit. They act as a check on the populations of the species they consume, such as regulating the prevalence of certain fish. As scavengers, they provide an additional service by removing the remains of deceased animals.