The Fox Sparrow (Passerella iliaca) is a large American sparrow. It is the only member of the genus Passerella, although some authors split the genus into four species (see below).

Adults are heavily spotted and streaked underneath. Plumage varies markedly from one group to another. More specific information regarding plumage is available in the accounts for the various taxa.

Fox Sparrow's nest in wooded areas across northern Canada and the west coast of North America from Alaska to California. They nest either in a sheltered location on the ground or low in trees or shrubs.

These birds migrate south on the west coast and to the eastern United States.

These birds forage by scratching the ground, which makes them vulnerable to cats and other predators, though they are generally plentiful. They mainly eat seeds and insects, also some berries. Birds on the coast may also eat crustaceans.

The review of Zink & Weckstein (2003) which added mtDNA cytochrome b, NADH dehydrogenase subunit 2 and 3, and D-loop sequence confirmed the 4 "subspecies groups" of the Fox Sparrow that were outlined by the initial limited mtDNA haplotype comparison (Zink 1994). These should probably be recognized as separate species, but this was deferred for further analysis of hybridization. Particularly the contact zones between the Slate-colored and Thick-billed Fox Sparrows which are only weakly distinct morphologically were of interest; the other groups were found to be distinct far earlier (Swarth 1920).

The combined molecular data is unable to resolve the interrelationship of the subspecies group and of subspecies in these, but aids in confirming the distinctness of the Thick-billed group (Zink & Weckstein 2003). Biogeography indicates that the coastal populations were probably isolated during an epoch of glaciation of the Rocky Mountains range, but this is also not very helpful in resolving the remaining problems of within-group diversity, and inter-group relationships.