The common reed warbler or Eurasian reed-warbler (Acrocephalus scirpaceus) is an Old World warbler in the genus Acrocephalus. It breeds across Europe into the temperate western Palaearctic where it is migratory, wintering in sub-Saharan Africa. It is also a resident species over large parts of Africa.

The common reed warbler was formally described in 1804 by the French naturalist Johann Hermann under the binomial name Turdus scirpaceus. The type locality is Alsace. The common reed warbler is now one of around 40 species placed in the genus Acrocephalus that was introduced by Johann Andreas Naumann and his son Johann Friedrich Naumann in 1811. The genus name Acrocephalus is from Ancient Greek akros, "highest", and kephalē, "head". It is possible that the Naumanns thought akro- meant "sharp-pointed," as in ἄκρα (akra, 'end, point'). The specific scirpaceus is from Latin and means "belonging to the bulrushes" (scirpus).

Ten subspecies are recognised:

An older scientific name for the reed warbler was Acrocephalus streperus (Vieill.).

The mostly resident Iberian and African subspecies are sometimes treated as a separate species, the African reed warbler (Acrocephalus baeticatus).

This is a medium-sized warbler, 13 cm (5.1 in) in length with a wing-span of 17–21 cm (6.7–8.3 in). The adult has an unstreaked brown back and buff underparts. The forehead is flattened, and the bill is strong and pointed. The sexes are identical, as with most warblers, but young birds are richer buff below. The common reed warbler looks similar to the great reed warbler, but the great reed warbler is larger in size and has a stronger supercilium.

The song is a slow, chattering jit-jit-jit with typically acrocephaline whistles and mimicry added.

This small passerine bird is a species found almost exclusively in reed beds, usually with some bushes. They can also be found in damp scrub.