The grass warblers are small passerine birds belonging to the genus Locustella of the Old World warbler family Sylviidae.

These are rather drab brownish warblers usually associated with fairly open grassland, shrubs or marshes. Some are streaked, others plain, all are difficult to view. They are insectivorous.

The most characteristic feature of this group is that the song of several species is a mechanical insect-like reeling which gives rise to the group's scientific name.

Species breeding in temperate regions are strongly migratory.

The nine species are

• Savi's Warbler, Locustella luscinoides
• Pallas's Grasshopper Warbler, Locustella certhiola
• Middendorf's Grasshopper Warbler , Locustella ochotensis
• Lanceolated Warbler, Locustella lanceolata
• River Warbler Locustella fluviatilis
• Gray's Grasshopper Warbler, Locustella fasciolata
• Grasshopper Warbler, Locustella naevia
• Styan's Grasshopper Warbler , Locustella pleskei
• Japanese Swamp Warbler , Locustella pryeri