Ceratioidei, the pelagic anglerfishes or deep-sea anglerfishes, is a suborder of marine ray-finned fishes, one of five suborders in the order Lophiiformes, the anglerfishes. These fishes are found in tropical and temperate seas throughout the world, living above the bottom of the deep sea, in the pelagic zone.

The deep-sea anglerfishes exhibit extreme sexual dimorphism; the males are many times smaller than the females. To reproduce, a male seeks out a female, using his sharp teeth-like denticles to clamp onto the female. The details of this sexual parasitism varies between the species; in a number of species the male permanently becomes part of the female, their tissues fusing with each other. This is the only known natural example of a process called parabiosis. The esca, the defining feature of all anglerfish groups, are bioluminescent in the deep-sea anglerfishes, attracting prey in the vast darkness of the bathypelagic zone which they inhabit.

Ceratioidei takes its name from the genus Ceratias, the type genus of the family Ceratiidae and of the suborder. Ceratias means "horn bearer", an allusion to the esca sticking up from the snout being likened to a horn.

Ceratioidei was first proposed as a grouping in 1912 by the English ichthyologist Charles Tate Regan as the division Ceratiformes within the suborder Lophoidea of the order Pediculati, which included the Batrachoididae. The Batrachoididae are no longer considered to be closely related to the anglerfishes, which are now included in the order Lophiiformes; within that clade the Ceratioidei are in the same clade as the Chaunacoidei with the Antennarioidei and the Ogcocephaloidei as the sisters of that clade. The 5th edition of Fishes of the World treats this grouping as a suborder within the Lophiiformes.

Classification of this suborder is largely based on characters specific to the females, such as the escal morphology, though some osteological characteristics and meristics are shared between the sexes. Male anglerfish can be identified to the genus level using characteristics of the denticular "teeth" and nostril morphology, but species-level identification has not been possible, even when examining parasitic males.

Ceratioidei contains the following families:

It is presumed that Ceratioids derive from an ancestor resembling modern Chaunacoids (deep-sea sea toads) or Ogcocephaloids (batfish), which lived in benthic or littoral habitats, which eventually retained the pelagic habits of the Lophiiform larva into adolescence. Monophyly is supported in this group through the shared characters of extreme sexual dimorphism, loss of the ambulatory pelvic fins found in other anglers, relocation of the pectoral fins, and a general reduction in density through the loss of bony parts, decrease in ossification and muscle mass, and the infusion of lipids throughout the body.

A 2024 study found that while the Ceratioids likely diverged from the Chaunacidae during the Paleocene, the diversification into their various extant families only occurred throughout the Eocene, following the Paleocene-Eocene Thermal Maximum. This likely also coincides with their colonization of deep sea habitats. Prior to these radiations, ancestral Ceratioids evolved extreme sexual size dimorphism and independently lost adaptive immune genes such as aicda, which allowed male anglerfishes to fuse with females, ultimately leading to the evolution of their sexual parasitism.