Xiphioidea is a clade of large pelagic teleosts characterized by extreme elongation of the premaxilla into a rigid bony rostrum (“bill”). Extant members are the swordfish, Xiphias (family Xiphiidae), and the sailfishes and marlins (family Istiophoridae).

Xiphioids are distinguished from other large predatory teleosts by their bony bill, loss of teeth in adults, and strongly reduced pelvic fins, which are entirely absent in Xiphias. Their streamlined bodies and lunate caudal fins reflect specialization for high-speed, open-ocean swimming.

The fossil record extends at least to the Paleogene and is dominated by isolated rostra, which preserve far more readily than the rest of the skeleton. Xiphioids are active pelagic predators, and the bill is interpreted primarily as a tool for striking or stunning prey rather than spearing it.