Various Passeriformes (perching birds) are commonly referred to as warblers. They are not necessarily closely related to one another, but share some characteristics, such as being fairly small, vocal, and insectivorous.

Sylvioid warblers

These are somewhat more closely related to each other than to other warblers. They belong to a superfamily also containing Old World babblers, bulbuls, etc.

Passeroid warblers

The two families of American warblers are part of another superfamily, which unites them with sparrows, buntings, finches, etc.

Other

These are closely related to the titmice and chickadees These are the most distinct group of warblers. They are not closely related at all to the others, but rather to the honeyeaters and fairy-wrens.