The Rufous-crowned Sparrow, Aimophila ruficeps, is a medium-sized sparrow. This passerine is primarily found across the Southwestern United States and much of the interior of Mexico, south to the transverse mountain range, and to the Pacific coast to the southwest of the transverse range. In the midwestern USA, the sparrow is found throughout central Oklahoma, and as far east as a small part of western Arkansas; its also found in a small region of northeastern Kansas, its most northeastern range.

The Rufous-crowned Sparrow was described in 1852 by John Cassin, and still bears its original binomial name of Aimophila ruficeps. The derivation of the genus name is from aimos/a?µ?? 'thicket' and phila/f??a 'loving'. Its specific epithet is a literal derivation of its common name, derived from the Latin words rufus 'rufous' and -ceps, from caput 'head'.

The Rufous-crowned Sparrow is a medium-sized sparrow at 5.25 inches (13.0 cm) in length. It has brown back with darker streaks and gray underparts. Its wings are brown and do not have wingbars. The sparrow's tail is long, brown, and rounded. The face and supercilium are gray with a brown or rufous steak extending from each eye and a thick black malar streak. This sparrow also has rusty crown which gives it its common name. The bill is yellow and conical shaped. Its legs and feet are pink-gray. Both sexes are similar in appearance, but the juvenile Rufous-crowned Sparrow has a brown crown and numerous streaks on its breast and flanks from spring to fall. Its voice has been described as a "chip-chip" call.

This bird is found in the southwestern United States and in Mexico. It lives in California, southern Arizona, southern New Mexico, Texas, and central Oklahoma south along Baja California and in western Mexico to southern Puebla and Oaxaca. The range of this species is discontinuous and is made up of many small, isolated populations in different locations. The Rufous-crowned Sparrow is a non-migratory species, though the mountainous subspecies are known to descend to lower elevations during severe winters.

The sparrow is found in open oak woodlands and dry uplands with grassy vegetation and bushes. It is often found near rocky outcroppings. The species is also known from coastal shrublands and chaparral areas.

The average territory size of Rufous-crowned Sparrows in the chaparral of California is 0.89 hectares (2.0 acres) to 1.5 hectares (4.0 acres). The density of Rufous-crowned Sparrow territories ranges by habitat, including 2.5 to 5.8 territories per 40 hectares (99.0 acres) of three to five year old burned chaparral to 3.9 to 6.9 territories for the same amount of coastal scrubland.

The Rufous-crowned Sparrow forages in pairs during the breeding season and in family-sized flocks in late summer and early fall. During the winter they can occasionally be found in loose mixed-species flocks.

This sparrow feeds primarily on small grass and forb seeds, fresh grass stems, and tender plant shoots during the fall and winter. During these seasons, insects such as ants, grasshoppers, ground beetles, and scale insects make up a small part of its diet. It the spring and summer, the bird feeds primarily on the same things, though it eats more insects and eats a more diverse array of species.

The Rufous-crowned Sparrow forages on or near the ground by walking or hopping under shrubs or dense grasses. Though they occasionally forage in weedy areas, they are almost never observed foraging in the open. They have also occasionally been observed feeding in branches and low shrubs. During the breeding season, they glean their food from grasses and low shrubs. Normally the species obtains its food by either pecking or less frequently scratching at leaf litter. This sparrow is a diurnal feeder.

It is unknown whether this species obtains all of its water from the food its eats or if it must drink; however, they have been observed both drinking and bathing in pools of water after rain storms.

The Rufous-crowned Sparrow breeds in successional scrubland. While it is not known when precisely the breeding season starts, the earliest that a sparrow has been observed carrying nesting material was on March 2 in southern California. It builds an open-cup nest close to or on the ground. It lays between two and five eggs at a time and may raise two broods a year.

The Rufous-crowned Sparrow is treated as a species of Least Concern by BirdLife International due to its large global range of 1,200,000 km², estimated population of 2,400,000 individuals, and lack of a 30% decline overall in the species's population over the last ten years. However, some of the local populations of this bird are threatened and declining in number. The island subspecies and populations have declined in some cases: A. r. sanctorum has not been seen on the Todos Santos Islands since the 1970s and the populations on Santa Catalina Island and Baja California's Islas de San Martin since the early 1900s. Populations of the species in southern California are also becoming more restricted in range because of urbanization and agricultural development in the region.