Cool season grasses generally do not persist well under the drought and heat stress that often occurs in the southern Great Plains. Mechanisms for overcoming such stresses are needed. A number of cool season perennial grass species display varying degrees of summer dormancy. Research conducted in Oklahoma and Texas over the past 5 years has examined the usefulness of summer dormancy as a mechanism for improving persistence of cool season perennial grasses. In grazing tolerance trials conducted in north Texas and southern Oklahoma, survival of summer dormant tall fescue was greater than 90% after two years, whereas stands for summer active tall fescues were far less, in some cases averaging less than 10%. Similar results occurred for summer dormant and summer active orchardgrass entries. Summer active tall fescues have persisted better and been more productive than summer dormant types under clipping in southern Oklahoma, however. In addition, summer dormant germplasm does not appear to be as winter hardy as the summer active types. Efforts are underway to identify additional summer dormant germplasm sources in tall fescue and other cool season grasses, and to incorporate the summer dormant trait into a number of tall fescue breeding populations.