The importance of shrub species and shrubland ecosystems gained considerable impetus about 30 years ago with the establishment of the USDA Forest Service Shrub Sciences Laboratory and a series of workshops and symposia that preceded and accompanied the establishment of the Laboratory. Since that time, the Shrub Research Consortium and other forums have addressed various aspects of wildland shrub ecosystem biology and management. Shrubs occur in most vegetation types but are dominants only in those habitats that place plants under considerable stress. Three primary, often interacting factors, that promote shrubby habitats are drought or aridity, nutrient-poor soils, and fire. Other stress factors that may also be interactive that contribute to the shrubby habitat are shade, poor soil aeration, winter cold, short growing season, and wind. Most of these conditions frequently occur in semi-arid, temperate, continental climates. The principal shrubland ecosystems of the western United States are sagebrush, chaparral, mountain brush, coastal sage, blackbrush, salt desert, creosote bush, palo verde-cactus, mesquite, ceniza shrub, shinnery, and sand-sage prairie. Similar as well as distinctively different shrubland ecosystems occur at other locations around the world. Shrubland ecosystems have different human and wildlife values and have, and are, subject to changing environmental conditions including different fire regimes. Fragmentations of these ecosystems, for example the sagebrush ecosystems, are of concern since some ecosystem components are at critical risk. Shrubland ecosystem changes have become more apparent in recent decades posing significant ecological and management problems. The challenge for land managers and ecologists is to understand the fluidity of the ecosystems and to be proactive and sensitive to the needs of healthy, productive landscapes.