Abstract U.S. military installations increasingly have become de facto bioreserves as the result of legacy and current land uses, urbanization, and historical siting of installations. The relative value of military lands as bioreserves compared to land holdings of other federal agencies is not proportional to total land area. Ironically, a significant reason that U.S. military installations have become important bioreserves is that they were not established with the purpose of conserving or extracting natural resources. This historical factor has resulted in a broad representation of U.S. ecoregions on military lands and largely has shielded those lands from the habitat loss and degradation that has occurred in surrounding regions due to urbanization, agricultural development, and other non-military land uses. Fort Hood, Texas, is used as a case study to illustrate the characteristics of military installations that fit the model for bioreserves as areas for conservation of biological resources and processes in the context of human use of the environment. A major current challenge for management of natural resources on military lands is that the value of U.S. military lands as bioreserves is increasing as surrounding habitats and natural communities continue to be degraded.