The vegetarian finch (Platyspiza crassirostris) is a species of bird in the Darwin's finch group of the tanager family Thraupidae endemic to the Galápagos Islands. It is the only member of the genus Platyspiza.

The vegetarian finch is one of Darwin's finches, a group of closely related birds that evolved on the Galápagos Islands. The group is related to the yellow-faced grassquit (Tiaris olivaceus) which is found in South and Central America and the Caribbean. An ancestral relative of the grassquit arrived on the Galápagos Islands some 2–3 million years ago, and the vegetarian finch is an early evolutionary radiation from that ancestor.

When Darwin first collected the species in 1835, he assumed it was a finch. John Gould, who formally described the vegetarian finch in 1837, placed it in a new genus Camarhynchus and coined the binomial name Camarhynchus crassirostris. The vegetarian finch is now placed in the genus Platyspiza that was introduced by Robert Ridgway in 1897. Molecular phylogenetic studies have shown that Darwin's "finches" are actually members of the subfamily Coerebinae within the large tanager family Thraupidae.

The vegetarian finch is the sole member of the genus Platyspiza, which some taxonomists still subsume into the genus Camarhynchus.

The genus name Platyspiza comes from the Greek platus, meaning "broad" and spiza, meaning "finch". The specific name crassirostris comes from the Latin crassus, meaning "heavy" or "thick" and rostris, meaning "-billed" (rostrum = bill). The "vegetarian" of its common name refers to its primary diet.

The vegetarian finch is one of the largest Galápagos finches, measuring 16 cm (6.3 in) in length and ranging from 29 to 40 g (1.0 to 1.4 oz) in mass. Its upright stance is described as "parrot-like". Its beak is broad and stout, with a strongly curved culmen. Males have upper parts which are olive-colored, with underparts that are whitish, with smudgy streaking on the lower breast and flanks; some birds show rufous on the underparts. Their lower flanks and undertail coverts are buffy, with a black hood, throat, breast and upper flanks. Their iris is dark, and the bill is black in the breeding season and horn-colored during the rest of the year. Females are principally brown above and off-white below, with a buffy rump and flanks streaked with brown on the face, crown, upperparts, throat, breast and flanks, and show two indistinct buffy wingbars on the brown wings. Their beak is two-toned; the upper mandible ranges in color from dusky brown to black, while the lower mandible is dull orange or dull pink. The immature male is intermediate in appearance between the adult male and the adult female; it appears blackish on the face and throat, but is more streaked below than the adult male.

The song of the vegetarian finch is nasal and drawn out, with each note lasting about two seconds. Transcribed as ph'wheeeuuuuu-íííúúú, it is accented towards the end. The bird's primary call is high-pitched and squealing, said to resemble the sound of a radio tuner. It also gives a whiny pheep.

Endemic to the Galápagos, the vegetarian finch is found on seven islands: San Cristóbal, Santa Cruz, Isabela, Marchena, Santiago, Pinta and Fernandina. It is found from 0 to 500 m (0 to 1,640 ft) above sea level. Although it is most common in montane evergreen forest, particularly the transition zone, its range also extends up into the humid zone and down into the arid zone. Although the vegetarian finch was previously found on Pinzón, Santa Fé, and Floreana, the species is now extirpated from these islands. On Floreana, the species was rarely observed in the second half of the 20th century, with the last reported sightings of single individuals in the agricultural zone in 2004 and at Cerro Pajas in 2008.