The Flint Hills, historically known as Bluestem Pastures or Blue Stem Hills are a region in eastern Kansas and north-central Oklahoma named for the abundant residual flint eroded from the bedrock that lies near or at the surface. It consists of a band of hills stretching from Kansas to Oklahoma. Oklahomans generally refer to the same geologic formation as the Osage Hills or the Osage.

The Flint Hills Ecoregion is designated as a distinct region because it has the densest coverage of intact tallgrass prairie in North America. Due to its rocky soil, the early settlers were unable to plow the area, resulting in the prevalence of cattle ranches as opposed to the crop land more typical of the Great Plains. These ranches rely on annual controlled burns conducted by ranchers every spring to renew the prairie grasses for cattle to graze.

The Flint Hills is a region of rolling hills with relatively narrow steep valleys, and is composed of shale and cherty limestone with rocky soils. In contrast to surrounding ecological regions that are mostly in cropland, most of the Flint Hills region is grazed by beef cattle.

The Flint Hills mark the western edge of the tallgrass prairie, and contain the largest remaining intact tallgrass prairie in the Great Plains.