Spizella breweri is a small, slim species of American sparrow in the family Emberizidae.

Adults have grey-brown backs and brown crowns, both with dark streaks, and a pale eye-ring. Their wings are brown with light wing bars and the underparts are pale grey. Their bill is pale with a dark tip and they have a long notched tail. They are similar in appearance to the Clay-colored Sparrow but do not have a pale stripe on the crown or grey neck patch.

There are two distinct subspecies:

Spizella breweri breweri, Brewer's Sparrow proper, is found in brushy areas, especially with sagebrush, in southern parts of western Canada and in the western United States.

Spizella breweri taverneri, the Timberline Sparrow, is found in thicketed areas around the tree line in the Rockies of northern British Columbia, the southern Yukon and southeastern Alaska. These birds are somewhat darker and larger than the southern subspecies.; some consider this to be a separate species.

These birds migrate to the southwestern United States south to central Mexico.

These birds forage primarily in shrubs or in low vegetation, but also on the ground. They mainly eat insects in summer with seeds becoming a more important part of the diet at other times of the year. They usually forage in flocks outside of the breeding season, sometimes with other sparrows.

The male sings to defend a nesting territory. The song is a long varied mix of notes and trills. Males have 2 distinct types of songs - classified as short and long songs. The female typically lays 3 to 4 eggs (up to 5) in a cup nest in low shrubs.

These birds have decreased in some parts of their range. Causes are not well understood, but it is suspected that the decline is due at least in part to destruction of sagebrush habitat. Additional information on resource use and limitation during the wintering season is desperately needed.

This bird was named after the ornithologist Thomas Mayo Brewer.