The passenger pigeon or wild pigeon (Ectopistes migratorius) is an extinct species of pigeon that was endemic to North America. Its common name is derived from the French word passager, meaning "passing by", due to the migratory habits of the species. The scientific name also refers to its migratory characteristics. The morphologically similar mourning dove (Zenaida macroura) was long thought to be its closest relative, and the two were at times confused, but genetic analysis has shown that the genus Patagioenas is more closely related to it than the Zenaida doves.

The passenger pigeon was sexually dimorphic in size and coloration. The male was 390 to 410 mm (15.4 to 16.1 in) in length, mainly gray on the upperparts, lighter on the underparts, with iridescent bronze feathers on the neck, and black spots on the wings. The female was 380 to 400 mm (15.0 to 15.7 in), and was duller and browner than the male overall. The juvenile was similar to the female, but without iridescence. It mainly inhabited the deciduous forests of eastern North America and was also recorded elsewhere, but bred primarily around the Great Lakes. The pigeon migrated in enormous flocks, constantly searching for food, shelter, and breeding grounds, and was once the most abundant bird in North America, numbering around 3 billion, and possibly up to 5 billion, “at the time of the discovery of America,” according to A. W. Schorger.

Though one genetic study concluded that the bird was not always that abundant, and that the population size fluctuated dramatically over time, a more recent study found evidence that this was not the correct interpretation of the genetic data, and instead concluded that the passenger pigeon population size had been stable for at least 20,000 years prior to "its 19th-century decline and eventual extinction." A very fast flyer, the passenger pigeon could reach a speed of 100 km/h (62 mph). The bird fed mainly on mast, and also fruits and invertebrates. It practiced communal roosting and communal breeding, and its extreme gregariousness may be linked with searching for food and predator satiation.

Passenger pigeons were hunted by Native Americans, but hunting intensified after the arrival of Europeans, particularly in the 19th century. Pigeon meat was commercialized as cheap food, resulting in hunting on a massive scale for many decades. There were several other factors contributing to the decline and subsequent extinction of the species, including shrinking of the large breeding populations necessary for preservation of the species and widespread deforestation, which destroyed its habitat. A slow decline between about 1800 and 1870 was followed by a rapid decline between 1870 and 1890. The last confirmed wild bird is thought to have been shot in 1901. The last captive birds were divided in three groups around the turn of the 20th century, some of which were photographed alive. Martha, thought to be the last passenger pigeon, died on September 1, 1914, at the Cincinnati Zoo. The eradication of this species is a notable example of anthropogenic extinction.