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Old World Bluestems (OWB), a group of non-native, invasive, warm-season grasses, have been extensively planted throughout the Central and Southern Great Plains for livestock forage production, perennial vegetation cover in the Conservation Reserve Program and erosion control. Examples of these grasses include Caucasian (Bothriochloa bladhii), yellow (Bothriochloa ischaemum) and Kleberg's (Dichanthium annulatum) bluestem. Each of these species have escaped from their planted boundary and invaded native grasslands, altering multiple trophic levels throughout their invaded range. Within the past 15 years research has focused on the effect of these grasses on various taxa rather than their use in agricultural production. Old World bluestems reduce native plant species diversity and seed bank composition, as well as change soil microbial communities in a manner that inhibits colonization by native grasses. Effects of exotic grass invasion on structural attributes of plant communities appear to vary with the invading species and the extent of the invasion, resulting in wide ranging effects on wildlife populations. Rodent communities in central Texas were found to have reduced species richness and abundance in OWB monocultures compared to habitats dominated by native grasses. In a mixed-grass prairie habitat in south central Kansas, bird species richness, bird abundance and food availability (arthropod biomass) were significantly lower in OWB monocultures than in native rangeland. Importantly, OWB monocultures had lower heterogeneity of vegetation structure, as well as fewer forbs than the native rangeland sites, potentially contributing to the reduced species richness and abundance of the grassland birds. Invasion by exotic grasses in the South-central United States has been proposed as a contributing factor in the decline of grassland birds; however, at a population level, individual bird species exhibit differing responses to the presence of exotic grasses and the level of invasion.