Catullus 3 is a poem by Roman poet Gaius Valerius Catullus (c. 84–c. 54 BCE) that laments the death of a pet sparrow (passer) for which an unnamed girl (puella), possibly Catullus' lover Lesbia, had an affection. Written in hendecasyllabic meter, it is considered to be one of the most famous of Latin poems.

This poem, together with Catullus' other poems, survived from antiquity in a single manuscript discovered c. 1300 in Verona, from which three copies survive. Fourteen centuries of copying from copies left scholars in doubt as to the poem's original wording in a few places, although centuries of scholarship have led to a consensus critical version. Research on Catullus was the first application of the genealogical method of textual criticism.

In the original manuscript, Catullus 3 and Catullus 2 were parts of the same text, but the two poems were separated by scholars in the 16th century.

The metric scheme is  ⏒ ⏒ | ‒ ⏑ ⏑ | ‒ ⏑ | ‒ ⏑ | ‒ ⏒ .

Ingleheart finds epigrammatic features in the poem, including a connection with Greek epigrams: the poem, starting with the first word, reads like an epitaph. Tradition of epigrams to dead pets was well established at the time (Thomas points to a potential borrowing from Meleager). The Hellenistic epigrams about dead pets are somewhat parodic, exploiting the disconnect between the ultimately serious topic of death and an insignificance of an animal. Catullus utilizes this effect to focus the attention of the reader on the girl, not the sparrow, producing a celebration of mea puella and essentially turning the girl's loss into his own gain with certain amount of mockery.

In the beginning of the poem, the poet "controls the proceedings", directing Venuses and Amores, and later all men of refine (venustiores) to mourn, following the script of Roman funerals, where a family member or a professional mourner (praefica) would ask the crowd to remember the loss. The fact that all the commotion is about a dead bird is quickly revealed; the standard eulogy would have proceeded along the standard Roman lines: genealogy (skipped in the poem, as pets – and slaves, that also could have been characterized as deliciae – were considered to be creations of their masters), deeds (also none), and character. The latter includes good disposition and loyalty, wording typical for epitaphs. At the end poet refers to the Hades and addresses the deceased in the second person, as was traditional for Roman laudatio funebris.

The traditional reading of the poem (and Catullus 2) is thus straightforward: the poet borrows from the literary tradition of using either a real (or a fictional) connection between a lover and her pet, so he can inject himself into the story as an observer and describe his own relationship with Lesbia. Pomeroy suggests that the poem also reflects on the power relationships in the Roman society, in particular, between a child slave (deliciae, symbolized by the bird) and their master.

Following the printing of Catullus' works in 1472, Poems 2 and 3 gained new influence and ignited the dispute on the meaning of the passer, with some scholars suggesting that the word did not mean a sparrow, but was a phallic symbol, particularly if sinu in line 2 of Catullus 2 is translated as "lap" rather than "bosom". Other scholars, however, have rejected this suggestion. Pomeroy suggests that the clearest arguments "for" belong to Giangrande and "against" – to Jocelyn, Thomas mentions also opposition from Adams, while Vergados and O'Bryhim highlight a collection of papers in a book by Gaisser. This reading of Catullus 3 suggests a description of the end of an amorous affair, while Catullus 2 provides the details of the sexual activities. In Hooper's interpretation, Catullus 3 is a lament about a temporary impotence.