The four Phocoena species are primarily fish eaters that usually swim in pairs or small groups along coastlines and occasionally in rivers. They are gray or black above and white below. Best known of these is the harbour porpoise, P. phocoena, a shy cetacean that generally avoids boats and rarely leaps above the water. It is found throughout much of the Northern Hemisphere and is hunted in some regions. During the Middle Ages this animal was considered a royal delicacy. The other members of the genus are more restricted in distribution. The vaquita, or cochito (P. sinus), is listed as a critically endangered species by the International Union for Conservation of Nature (IUCN). Vaquitas are found only near the northern end of the Gulf of California (California, Gulf of). Burmeister's porpoise (P. spinipinnis) has blunt tubercles on its dorsal fin and lives off the coasts of eastern and western South America. The spectacled porpoise (P. dioptrica, sometimes referred to as Australophocaena diotropica) is named for the patchlike pigmentation pattern around its eyes and is distributed throughout the southern Indian, Atlantic, and Pacific oceans.

The Dall porpoise (Phocoenoides dalli) is the largest porpoise and the only member of its genus. Active and gregarious, it often rides the bow waves of ships. The Dall porpoise is black with a large white patch on each side of the body. It is usually seen in groups of 2 to 20 along the northern rim of the Pacific Ocean, where they eat squid and fish. True's porpoise (P. dalli truei) is considered by some authorities to be a separate subspecies and is distinguished from the Dall porpoise by its absence of the striking white body patches. It is found only near Japan.

The finless porpoise (Neophocaena phocaenoides) is a small, slow-moving inhabitant of coastal waters and rivers along the Indian Ocean and western Pacific Ocean. Black above and white below, it has a rounded head. Unlike other porpoises, it lacks a dorsal fin entirely. The finless porpoise lives alone or in small groups and eats crustaceans, fish, and squid.

Members of the family Phocoenidae are related to the oceanic dolphins (family Delphinidae), river dolphins (river dolphin), and other toothed whales of the suborder Odontoceti. The common name is derived from the Latin porcus (“hog” or “pig”) and piscinus (“fish”), as their flesh was said to taste somewhat like pork.