Leaf warblers are small insectivorous passerine birds belonging to the genus Phylloscopus.
Leaf warblers were formerly included in the Old World warbler family but are now considered to belong to the family Phylloscopidae, introduced in 2006. The family originally included the genus Seicercus, but all species have been moved to Phylloscopus in the most recent classification. Leaf warblers are active, constantly moving, often flicking their wings as they glean the foliage for insects along the branches of trees and bushes. They forage at various levels within forests, from the top canopy to the understorey. Most of the species are markedly territorial both in their summer and winter quarters. Most are greenish or brownish above and off-white or yellowish below. Compared to some other "warblers", their songs are very simple. Species breeding in temperate regions are usually strongly migratory.
Its members occur in Eurasia, ranging into Wallacea and Africa with one species, the Arctic warbler, breeding as far east as Alaska. Many of the species breed at temperate and high latitudes in Eurasia and migrate substantial distances to winter in southeastern Asia, India, or Africa. One example is Tickell's leaf warbler, which breeds in scrub at high elevation in the Himalayas and on the Tibetan Plateau and then moves down-slope and south to winter in the Himalayan foothills of India and Burma. Most live in forest and scrub and many are canopy or sub-canopy dwellers.