The Blue-and-yellow Tanager (Thraupis bonariensis) is a species of bird in the Thraupidae family, the tanagers. It is found in Argentina, Uruguay, Brazil, Paraguay, Bolivia, extreme northern border Chile, and Andean Peru and Ecuador. Some southern region birds migrate northeastwards in the austral winter into eastern Bolivia and northeastern Argentina; also Paraguay where the birds are only migratory non-breeding residents. Males of the eastern nominate group have a black back, while the members of the western darwinii group have a green back. The latter has been considered a separate species, the Darwin's Tanager (Thraupis darwinii).
Its natural habitats are subtropical or tropical dry forests, subtropical or tropical moist lowland forests, subtropical or tropical moist montanes, subtropical or tropical high-altitude shrubland, and heavily degraded former forest.