Olive green color, dorsoventrally flattened body, a beaked head, short neck and well developed paddle-like arms for swimming. Green sea turtle have a short head and unhooked beaks unlike the closely related hawksbill turtles. They have 2 long prefrontal scales between they eyes in stead of 4, the carapace is composed of 5 central, non-overlapping plates (or scutes), each flanked by 4 big lateral plates, and 12 small marginal scutes from head to tail on the edges. The carapace has color patterns that change over time but have outward radiating stripes or dark blotches, the belly (plastrons) is yellow to white. Juveniles are almost entirely black with white to yellow plastrons, when they turn juvenile the black color changes to olive.

Listed as endangered on the IUCN Red list. Global populations show a strong decrease, and the number of nesting females has dropped between 50 and 70% in the last 30 years. Collection of turtle eggs from nesting grounds poses a threat to their survival, loss of empty beaches to lay their eggs or degradation of their habitat as well as bycatch or entanglement in marine fisheries by drift netting, shrimp trawling, dynamite fishing, and long-lining. Also light pollution is a threat to hatchlings. They use moonlight for orientation towards the sea, but are distracted and drawn away by lights on or near the beach, which is often fatal.

Distributed widely in tropical and subtropical waters. 2 Subpopulations exist, each with their own nesting and feeding grounds, one in the Atlantic, the other in the Pacific. Hatchlings are pelagic, juveniles and adults are mostly found on or near inshore reefs (eating algae) or seagrass beds. From birth to adulthood they live in a depth range of 0-200 meters.

Green sea turtles breed in cycles of 1-4 years, and can change cycles depending on age and food quantity and quality. They can lay several hundreds of eggs each time, but only  a small percentage of hatchlings reaches maturity. They return to the same beaches where they were born to lay their own eggs. Green sea turtles show distinctive courting behavior in coastal regions after which the females emerge from the water to dig a pit to lay her eggs. She covers the eggs with sand when she is done. Males are polygamous and will try to mate with several females in the same nesting season to increase their chances of offspring.