The Acrocephalus warblers are small, insectivorous passerine birds belonging to the genus Acrocephalus of the Old World warbler family Sylviidae. They are sometimes called marsh warblers or reed warblers, but this invites confusion with Marsh Warbler and Reed Warbler, especially in North America where it is common to use lower case for bird species.

These are rather drab brownish warblers usually associated with marshes or other wetlands. Some are streaked, others plain. Almost all are migratory.

Many species have a flat head profile, which gives rise to the group's scientific name.

Species breeding in temperate regions are strongly migratory.

The 35 species are

• Moustached Warbler, Acrocephalus melanopogon
• Aquatic Warbler, Acrocephalus paludicola
• Sedge Warbler, Acrocephalus schoenobaenus
• Streaked Reed Warbler, Acrocephalus sorghophilus
• Black-browed Reed Warbler, Acrocephalus bistrigiceps
• Paddyfield Warbler, Acrocephalus agricola
• Blunt-winged Warbler, Acrocephalus concinens
• Reed Warbler, Acrocephalus scirpaceus
• African Reed Warbler, Acrocephalus baeticatus
• Blyth's Reed Warbler, Acrocephalus dumetorum
• Marsh Warbler, Acrocephalus palustris
• Great Reed Warbler, Acrocephalus arundinaceus
• Oriental Reed Warbler, Acrocephalus orientalis
• Clamorous Reed Warbler, Acrocephalus stentoreus
• Large-billed Reed Warbler, Acrocephalus orinus
• Basra Reed Warbler, Acrocephalus griseldis
• Australian Reed Warbler, Acrocephalus australis
• Nightingale Reed Warbler, Acrocephalus luscinia
• Caroline Reed Warbler, Acrocephalus syrinx
• Nauru Reed Warbler, Acrocephalus rehsei
• Millerbird, Acrocephalus familiaris
• Christmas Island Warbler, Acrocephalus aequinoctialis
• Tahiti Reed Warbler, Acrocephalus caffer
• Tuamotu Reed Warbler, Acrocephalus atyphus
• Rimitara Reed Warbler, Acrocephalus rimitarae
• Pitcairn Reed Warbler, Acrocephalus vaughani
• Henderson Island Reed Warbler, Acrocephalus taiti
• Marquesan Reed Warbler, Acrocephalus mendanae
• Cook Islands Reed Warbler, Acrocephalus kerearako
• Greater Swamp Warbler, Acrocephalus rufescens
• Cape Verde Swamp Warbler, Acrocephalus brevipennis
• Lesser Swamp Warbler, Acrocephalus gracilirostris
• Madagascar Swamp Warbler, Acrocephalus newtoni
• Thick-billed Warbler, Acrocephalus aedon
• Rodrigues Brush Warbler, Acrocephalus rodericanus
• Seychelles Brush Warbler, Acrocephalus sechellensis