Pinnipedia is an infraorder of mammals in the order Carnivora, composed of seals, sea lions, and the walrus. A member of this group is called a pinniped or a seal.^{[lower-alpha 1]} They are widespread throughout the ocean and some larger lakes, primarily in colder waters. Pinnipeds range in size from the 1.1 m (3 ft 7 in) and 50 kg (110 lb) Baikal seal to the 6 m (20 ft) and 3,700 kg (8,200 lb) male southern elephant seal, which is also the largest member of Carnivora.^[1] Several species exhibit sexual dimorphism, such as the southern elephant seal, where the males can be more than three times as long and six times as massive as the females, or the Ross seal, which has females typically larger than the males. Four seal species are estimated to have over one million members, while six are classified as endangered with population counts as low as 600, and two, the Caribbean monk seal and the Japanese sea lion, went extinct in the 20th century.

The 34 extant species of Pinnipedia are split into 22 genera within 3 families: Odobenidae, comprising the walrus; Otariidae, the eared seals, split between the sea lions and fur seals; and Phocidae, the earless or true seals. Odobenidae and Otariidae are combined into the superfamily Otarioidea, with Phocidae in Phocoidea. Extinct species have also been placed into the three extant families, as well as the extinct family Desmatophocidae, though most extinct species have not been categorized into a subfamily. Nearly one hundred extinct Pinnipedia species have been discovered, though due to ongoing research and discoveries the exact number and categorization is not fixed.

Conservation status codes listed follow the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Range maps are provided wherever possible; if a range map is not available, a description of the pinniped's range is provided. Ranges are based on the IUCN Red List for that species unless otherwise noted. All extinct species or subspecies listed alongside extant species went extinct after 1500 CE, and are indicated by a dagger symbol "†".

The infraorder Pinnipedia consists of 3 families containing 34 extant species belonging to 22 genera and divided into 48 extant subspecies, as well the extinct Caribbean monk seal and Japanese sea lion species, which are the only pinniped species to go extinct since prehistoric times. This does not include hybrid species or extinct prehistoric species.

The following classification is based on the taxonomy described by Mammal Species of the World (2005), with augmentation by generally accepted proposals made since using molecular phylogenetic analysis. This includes splitting the monk seal genus Monachus into Monachus and Neomonachus, the reorganization of grey seal subspecies, and the removal of the Laptev walrus subspecies.^[2][3][4]