The genus Phaethon was introduced in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae.

[4] The type species was designated as the red-billed tropicbird (Phaethon aethereus) by George Robert Gray in 1840.

[7] 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.

The legs of a tropicbird are located far back on their body, making walking impossible, so that they can only move on land by pushing themselves forward with their feet.

[10] Tropicbirds tend to avoid multi-species feeding flocks, unlike the frigatebirds, which have similar diets.

It will stay alone in the nest while both parents search for food, and they will feed the chick twice every three days until fledging, about 12–13 weeks after hatching.

Tropicbird chicks have slower growth than nearshore birds, and they tend to accumulate fat deposits while young.

That, along with one-egg clutches, appears to be an adaptation to a pelagic lifestyle where food is often gathered in large amounts, but may be hard to find.