In males the testes are internal and the baculum is well developed. The upper incisors have a simple pointed crown, the canines are elongate, and the postcanines usually have three or more distinct cusps. Phocids shelter on rocky or sandy coasts, islands, and ice floes. Some stay on land or ice much of the time. Some migrate or disperse over a large area, and others make local movements corresponding to fluctuations of the ice.
Activity is both diurnal and nocturnal.
Olfaction may be important in communicating intraspecific information. Phocids defend themselves by opening their mouth, uttering menacing cries, and advancing against the enemy, or they may flee to the water and dive. Most species eat fish, shellfish, and cephalopods. Hydrurga is the only pinniped that preys regularly on penguins and other seals. Some species can fast for long periods.