Tropicbirds were traditionally grouped in the order Pelecaniformes, which contained the pelicans, cormorants and shags, darters, gannets and boobies and frigatebirds; in the Sibley–Ahlquist taxonomy, the Pelecaniformes were united with other groups into a large "Ciconiiformes".
More recently this grouping has been found to be massively paraphyletic (missing closer relatives of its distantly related groups) and split again.

Microscopic analysis of eggshell structure by Konstantin Mikhailov in 1995 found that the eggshells of tropicbirds lacked the covering of thick microglobular material of other Pelecaniformes.
Jarvis, et al.
's 2014 paper "Whole-genome analyses resolve early branches in the tree of life of modern birds" aligns the tropicbirds most closely with the sunbittern and the kagu of the Eurypygiformes, with these two clades forming the sister group of the "core water birds", the Aequornithes, and the Metaves hypothesis abandoned.

Order Phaethontiformes
Family †Prophaethontidae Harrison & Walker 1976
Genus †Prophaethon Andrews 1899
†Prophaethon shrubsolei Andrews 1899
Genus †Lithoptila Bourdon, Bouya & Iarochène 2005
†Lithoptila abdounensis Bourdon, Bouya & Iarochène 2005
Family Phaethontidae Brandt 1840
Genus †Proplegadis Harrison & Walker 1971
†Proplegadis fisheri Harrison & Walker 1971
Genus †Phaethusavis Bourdon, Amaghzaz & Bouya 2008
†Phaethusavis pelagicus Bourdon, Amaghzaz & Bouya 2008
Genus †Heliadornis Olson 1985
†H. ashbyi Olson 1985
†H. minor Kessler 2009
†H. paratethydicus Mlíkovský 1997
Genus Phaethon Linnaeus, 1758
Red-billed tropicbird P. aethereus (tropical Atlantic, eastern Pacific, and Indian oceans)
Red-tailed tropicbird, P. rubricauda (Indian Ocean and the western and central tropical Pacific)
White-tailed tropicbird, P. lepturus (widespread in tropical waters, except in the eastern Pacific)
The red-billed tropicbird is basal within the genus.
The split between the red-billed tropicbird and the other two tropicbirds is hypothesized to have taken place about six million years ago, with the split between the red-tailed and white-tailed tropicbird taking place about four million years ago.

Phaethusavis and Heliadornis are prehistoric genera of tropicbirds described from fossils.
Tropicbirds were traditionally grouped in the order Pelecaniformes, which contained the pelicans, cormorants and shags, darters, gannets and boobies and frigatebirds; in the Sibley–Ahlquist taxonomy, the Pelecaniformes were united with other groups into a large "Ciconiiformes". More recently this grouping has been found to be massively paraphyletic (missing closer relatives of its distantly related groups) and split again.
Microscopic analysis of eggshell structure by Konstantin Mikhailov in 1995 found that the eggshells of tropicbirds lacked the covering of thick microglobular material of other Pelecaniformes. Jarvis, et al.'s 2014 paper "Whole-genome analyses resolve early branches in the tree of life of modern birds" aligns the tropicbirds most closely with the sunbittern and the kagu of the Eurypygiformes, with these two clades forming the sister group of the "core water birds", the Aequornithes, and the Metaves hypothesis abandoned.
Order Phaethontiformes
Family †Prophaethontidae Harrison & Walker 1976
Genus †Prophaethon Andrews 1899
†Prophaethon shrubsolei Andrews 1899
Genus †Lithoptila Bourdon, Bouya & Iarochène 2005
†Lithoptila abdounensis Bourdon, Bouya & Iarochène 2005
Family Phaethontidae Brandt 1840
Genus †Proplegadis Harrison & Walker 1971
†Proplegadis fisheri Harrison & Walker 1971
Genus †Phaethusavis Bourdon, Amaghzaz & Bouya 2008
†Phaethusavis pelagicus Bourdon, Amaghzaz & Bouya 2008
Genus †Heliadornis Olson 1985
†H. ashbyi Olson 1985
†H. minor Kessler 2009
†H. paratethydicus Mlíkovský 1997
Genus Phaethon Linnaeus, 1758
Red-billed tropicbird P. aethereus (tropical Atlantic, eastern Pacific, and Indian oceans)
Red-tailed tropicbird, P. rubricauda (Indian Ocean and the western and central tropical Pacific)
White-tailed tropicbird, P. lepturus (widespread in tropical waters, except in the eastern Pacific)
The red-billed tropicbird is basal within the genus. The split between the red-billed tropicbird and the other two tropicbirds is hypothesized to have taken place about six million years ago, with the split between the red-tailed and white-tailed tropicbird taking place about four million years ago.
Phaethusavis and Heliadornis are prehistoric genera of tropicbirds described from fossils.
Tropicbird