Information on the historical variability of ecosystem conditions and the natural disturbance regimes that influence such variability is increasingly used in design of ecosystem management systems. The rationale for this approach is, in part, that species have adapted to habitat and disturbance conditions of previous millennia, and increased deviation from those conditions is likely to result in increased risk of species loss and other undesirable ecological change. Use of information on natural variability is challenged by (1) limits in our ability to interpret past ecosystem variability, (2) effects of environmental conditions (e.g., climate change, exotic species, and engineered structures) on ecosystems that move those systems outside the range of historical variability, and (3) limited public participation in formulating ecosystem management and using information on natural variability. Despite these difficulties, the concept of natural variability is finding important application in ecosystem assessment and design. Broad-scale, cursory analysis of ecosystem dynamics complements intensive analysis in areas of 10,000 to 100,000 acres. Extensive analysis gives a broad geographic context, and intensive analysis provides detailed knowledge of a longer record including low to moderate severity events.