Grasslands are the most abundant habitat type in Theodore Roosevelt National Park. Grasses are able to cope with the low annual precipitation, going dormant as the relatively wet spring gives way to the dry and hot summer.  To the untrained eye, grasslands may appear monotonous, but a rich diversity of plants survive in an intricate and ever-changing ecosystem that supports many of the park's animals.

A dozen native grasses and fifty different species of forbs and shrubs found in grasslands comprise the most diverse array of plant life in the park. Grasses including saltgrass, Western wheatgrass, needle-and-thread, and little bluestem provide valuable forage for a number of grazing animals such as bison, wild horses, elk, mule deer, and prairie dogs, not to mention a rich array of insect life. The grazing animals and insects of the grassland in turn attract predators; prairie dogs are under constant threat from badgers, coyotes, hawks, and eagles, and insects are eaten by birds such as flycatchers and swallows.

Over time, woodier plants such as sagebrush and wild rose become established in grasslands, changing the forage available to grazing animals. Periodic fire, whether natural or prescribed by the park, is necessary to improve habitat diversity and forage diversity. Fires reduce woody vegetation and allow early successional grasses and forbs to re-establish themselves.