There are two species of elephant seal. They are the sole members of the genus Mirounga of the family Phocidae or "true seals".

The species are the Northern Elephant Seal, Mirounga angustirostris, and the Southern Elephant Seal, M. leonina. Both species were hunted nearly to extinction by the end of the nineteenth century but numbers have since recovered. The Southern Elephant Seal is somewhat the bigger of the two.

The elephant seals get their name from their great size and the fact that the adult males have a large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating season. Elephant seals are also quite large, as the largest known bull elephant seal was 22 feet (6.7 m) in length and weighed 7,500 lb (3,400 kg).

Elephant seals spend an unusual amount of time in the ocean—up to 80% of their lives. They can hold their breath for up to 80 minutes, which is longer than any other mammal. Furthermore, elephant seals are incredible divers as well, with an ability to dive as deep as 5,000 feet (1,500 m) beneath the ocean's surface. The average depth of their dives is about 1,000 to 2,000 feet (300 to 600 m), as they search for their favorite foods, which are skates, rays, squid, octopi, eels, and small sharks.

Life expectancy: Female elephant seals have an average life expectancy of about 20 years, and can give birth starting at the age of 3–4. Males reach maturity at five years, but generally don't achieve alpha status until the age of 8, with the prime breeding years being between ages 9 and 12. The average life expectancy of a male elephant seal is 14 years.