Passer is a genus of sparrows, also known as the true sparrows. The genus contains 28 species and includes the house sparrow and the Eurasian tree sparrow, two of the most common birds in the world. They are small birds with thick bills for eating seeds, and are mostly coloured grey or brown. Native to the Old World, some species have been introduced throughout the world.
Most of its members are found naturally in open habitats in the warmer climates of Africa and southern Eurasia. Evolutionary studies suggest the genus originated in Africa. Several species have adapted to human habitation, and this has enabled the house sparrow in particular, in close association with humans, to extend its Eurasian range well beyond what was probably its original home in the Middle East. Apart from this natural colonisation, the house sparrow has been introduced to many parts of the world outside its natural range, including the Americas, sub-Saharan Africa, and Australia. The Eurasian tree sparrow has also been artificially introduced on a smaller scale, with populations in Australia and locally in Missouri and Illinois in the United States.