The etymology of the name remains uncertain. A frequently proposed connection derives it from the Greek seirá ("rope") and eírō ("to tie"), yielding a meaning along the lines of "binder" or "entangler" — a reading some link to Odysseus being bound to his mast as he passed them.

The term later became synonymous with the mermaid. Combining a human upper body with a fish's tail, this hybrid form became iconic in the Middle Ages through its treatment in the Physiologus and in the bestiaries that descended from it.

Homer's Odyssey gives no physical description of the Sirens, leaving their appearance to the reader's imagination. From the 7th century BCE they were regularly depicted in art as human-headed birds, and Apollonius of Rhodes described them as part woman and part bird. Early Greek art showed large birds with women's heads, bird feathers, and scaly feet; later depictions gave them human upper bodies with bird legs, often playing musical instruments, especially the lyre. The 10th-century Suda described them as having the form of sparrows from the chest up, or as little birds with women's faces. Male Sirens disappeared from art around the 5th century BCE.

Some Classical examples already showed Sirens in a mermaid-like form. The earliest known literary attestation of Sirens as mermaids is in the Anglo-Latin Liber Monstrorum (early 8th century), which describes them as sea-girls with the body of a maiden but the scaly tails of fishes. The 9th-century Bern Physiologus depicts them as half-woman, half-fish, while still retaining bird-like parts such as wings and clawed feet.

Family. Sophocles made Phorcys their father, but they are typically described as the daughters of the river god Achelous — by one of the Muses (Terpsichore, Melpomene, or Calliope) or by Sterope. Epimenides made them children of Oceanus and Gaia, and Euripides' Helen calls them winged maidens, daughters of the Earth.

Number and names. The Sirens' number varies from two to eight across sources. Homer's Odyssey speaks of two without naming them. Later writers give varying lists, including Peisinoe, Aglaope, and Thelxiepea; Parthenope, Ligeia, and Leucosia; and others such as Molpe, Himerope, and Aglaophonos.

Demeter. According to Ovid, the Sirens were companions of the young Persephone, and Demeter gave them wings to search for her after Hades carried her off. Hyginus instead has Demeter curse them for failing to intervene, decreeing that they should live only until a mortal who heard their song managed to pass them by.

The Muses. A statue at a sanctuary of Hera showed the goddess holding Sirens. By one account Hera urged the Sirens to enter a singing contest with the Muses; when the Muses won they plucked out the Sirens' feathers and made crowns from them. The Sirens cast off their remaining feathers, turned white, and threw themselves into the sea, giving rise to the place name Aptera ("featherless").

Argonautica. In Apollonius's Argonautica, the Argonauts' own Orpheus played his music more beautifully than the Sirens, drowning out their voices. Only the crewman Butes heard them and leapt into the sea, but he was caught up and carried safely away by the goddess Aphrodite.

Odyssey. Curious to hear their song, Odysseus followed Circe's advice: his sailors plugged their ears with beeswax and bound him to the mast. Though he signaled desperately to be freed, they bound him tighter, and released him only once the ship had passed. Some post-Homeric sources claim the Sirens were fated to die if anyone heard their singing and escaped.

Pliny. Pliny the Elder dismissed Sirens as pure fable, while noting claims that they existed in India, where they charm men with their song, lull them to sleep, and then tear them to pieces.

Funerary Siren statues appear throughout classical Greece and Magna Graecia, suggesting psychopomp characteristics — guiding the dead on the journey to the afterlife. The scholar Walter Copland Perry observed that their song was irresistibly sweet yet sad, inducing a fatal lethargy that was the forerunner of death and corruption; their song, in some readings, continually calls on Persephone.

The phrase "siren song" has come to mean an appeal that is hard to resist but that, if heeded, leads to a bad end. Jane Ellen Harrison noted that the Sirens appeal to the spirit rather than the flesh, functioning as mantic creatures like the Sphinx, knowing both the past and the future.

In Hebrew tradition reflected in the Book of Enoch, women led astray by the fallen angels were said to be turned into Sirens. Saint Jerome used "sirens" to translate Hebrew words for jackals and owls in biblical texts, and Christian writers such as Clement of Alexandria and Ambrose allegorized the Siren as a beautiful courtesan symbolizing worldly temptation. Isidore of Seville offered a euhemerist reading: the Sirens were prostitutes who led travelers down into poverty, given wings and claws because love flies and wounds.

Sirens and onocentaurs appear together in the Physiologus and the Latin bestiaries that followed it. The 9th-century Bern Physiologus illustrated them as mermaids despite text describing avian forms, and a 13th-century English bestiary likewise showed a group of Sirens as fish-tailed mermaids though its text called them winged fowl. Later bestiaries increasingly drew them as woman-fish hybrids, often holding a comb or mirror, attributes that became emblematic of mermaids across Europe.

Medieval and later literature continued to conflate Sirens with mermaids while citing the Physiologus. Dante's Purgatorio depicts a deformed Siren who becomes desirable when gazed upon and falsely claims to have turned Ulysses from his course. Geoffrey of Monmouth's Historia Regum Britanniae has Brutus encounter Sirens at the Pillars of Hercules who nearly overturn his ships. In the Renaissance the Siren became associated with female court musicians and was seen as a creature able to control a man's reason; Leonardo da Vinci wrote that she lulls mariners to sleep and then climbs aboard to kill them. In the Age of Exploration some Jesuit writers asserted that Sirens really existed, while later commentators such as Charles Burney and John Lemprière rationalized the myth as a memory of seductive singers or women on the coast of Sicily.

The Sirens have inspired numerous musical works. Claude Debussy's orchestral Nocturnes include a movement titled "Sirènes," evoking the sea, its rhythms, and the mysterious song of the Sirens. Lili Boulanger composed "Les sirènes" (1911) for mezzo-soprano, choir, and piano, and Alma Deutscher wrote an orchestral "Waltz of the Sirens."

In painting, William Etty's The Sirens and Ulysses (1837) portrayed them as young women in fully human form, a convention copied by later artists including Léon Belly, Edward Armitage, John William Waterhouse, and Herbert James Draper.