The common term 'warbler' is used as part of the name, or the general term, for most species of three different groups of birds of the suborder Oscines (order Passeriformes) which are (superficially) very alike, but because of anatomical and geographical reasons placed in three different (sub)families: 1) Sylviinae subfamily (over 300 species!) or 'Old World warblers' of the family Muscicapidae, 2) Parulidae family (about 115 species) or 'American warblers' or 'wood-warblers' and 3) Malurinae subfamily or 'Australian warblers' or 'wren-warblers' of the family Muscicapidae; these are better known under the name 'wren' or 'Australian wrens' in general and not further discussed here. Old World warblers are mainly distinguished from wood-warblers by having 10 primaries (flight-feathers, see wing) instead of 9. They are of small or very small size (from 8,9 cm), plainly coloured (usually greenish, brownish or pale greyish, except some more tropical species) and have fine, narrowly pointed bills. They are mostly insectivorous and arboreal (living in trees/woods). In most species there is no plumage difference between males and females, and many species resemble each other closely, so that identification becomes a matter for experts. However, identification can sometimes be facilitated by striking specific differences in the song which is often melodious and varied. Warblers are distributed throughout the Old World and the species living in cold and temperate regions are migratory (because of insect diet), wintering in tropical Africa (European warblers) or tropical Asia and New Guinea. They differ from the flycatchers (subfamily Muscicapinae) and the thrushes (subfamily Turdinae) of the same Muscicapidae family, in having an unspotted juvenile plumage resembling the adult plumage. Subdivisions can be made into: typical warblers, reed warblers, leaf warblers (genus Phylloscopus), wren-warblers, grass-warblers, ground warblers (genus Tesia) and tit-warblers (genus Leptopoecile). Wood-warblers belong to the great, complex group of New World 9-primaried song-birds that includes also such groups as the tanagers (Thraupinae family), honey-creepers (Coerebinae) and troupials (Icteridae), between which it is sometimes difficult to make divisions into families and various views on this matter are therefore possible. They are often brightly coloured, small birds (the largest being little larger than the House Sparrow Passer domesticus) and are mainly insectivorous, but some add berries and other vegetable matter to their diet. Wood-warblers are widely distributed ecologically (from swamps to deserts) and geographically from Alaska to southern South America.

Alternative forms for warblers : leaf warbler, leaf warblers, reed warbler, reed warblers, warbler.