Pisaster (from Greek πίσος, "pea", and ἀστήρ, "star") is a genus of Pacific sea stars that includes three species, P. brevispinus, P. giganteus, and P. ochraceus. Their range extends along the Pacific coast from Alaska to southern California in the intertidal zone. The largest individuals of Pisaster can reach diameters of up to 70 cm (28 in) across; they all develop five arms, but some may be lost from injury or disease, and occasionally the re-growth of an injured arm will result in an individual with more than five arms.

Sea stars in the genus Pisaster are all predators; the ochre sea star is the best-characterized of these, and is considered a "keystone" predator that controls the relative abundance of many other species in the ecosystem.