The baya weaver (Ploceus philippinus) is a weaverbird found across the Indian subcontinent and Southeast Asia. Flocks are found in grasslands, cultivated areas, scrub and secondary growth. They are known for their hanging retort shaped nests woven from leaves, usually found on thorny trees or palm fronds, near or hanging over water where predators cannot easily reach. They are widespread and common within their range and are prone to local, seasonal movements in response to rain and food availability.

Five subspecies are recognised. The nominate race P. p. philippinus is found through much of mainland India while P. p. burmanicus is found eastwards into Southeast Asia. The population in southwest India is darker above and referred to as subspecies P. p. travancoreensis.

In 1760, French zoologist Mathurin Jacques Brisson described the baya weaver in his Ornithologie based on a specimen he believed, incorrectly, to have been collected in Philippines. He used the French name Le gros-bec des Philippines and the Latin Coccothraustes Philippensis. Brisson's Latin names do not conform to the binomial system and are not recognised by the International Commission on Zoological Nomenclature. In 1776, Carl Linnaeus updated his Systema Naturae for the twelfth edition, including the baya weaver for which he coined the binomial name Loxia philippina. It was subsequently realised that Brisson was mistaken in believing that his specimen came from the Philippines and the type locality was redesignated as Sri Lanka. This species is now placed in the genus Ploceus that was introduced by the French naturalist Georges Cuvier in 1816.

There are five subspecies:

These are sparrow-sized (15 cm [5.9 in]) and in their non-breeding plumage, both males and females resemble female house sparrows. They have a stout conical bill and a short square tail. Non-breeding males and females look very similar: dark brown streaked fulvous buff above, plain (unstreaked) whitish fulvous below, eyebrow long and buff coloured, bill is horn coloured and no mask. Breeding males have a bright yellow crown, dark brown mask, blackish brown bill, upper parts are dark brown streaked with yellow, with a yellow breast and cream buff below.

Baya weavers are social and gregarious birds. They forage in flocks for seeds, both on the plants and on the ground. Flocks fly in close formations, often performing complicated manoeuvres. They glean paddy and other grain in harvested fields, and are sometimes considered pests for occasionally damaging ripening crops. They roost in reed-beds bordering waterbodies. They depend on wild grasses such as Guinea grass (Panicum maximum) as well as crops like rice for both their food (feeding on seedlings in the germination stage as well as on early stages of grain) and nesting material. They also feed on insects including butterflies, sometimes taking small frogs, geckos and molluscs, especially to feed their young. Their seasonal movements are governed by food availability. Their calls are a continuous chit-chit-... sometimes ending in a wheezy cheee-eee-ee that is produced by males in a chorus. A lower intensity call is produced in the non-breeding season.

They occasionally indulge in dust bathing.

In captivity, individuals form stable peck orders.