Knowing the condition of natural resources in national parks is fundamental to the National Park Service's (NPS) ability to manage park resources "unimpaired for the enjoyment of future generations." Beginning in 1992, with additional support by the 1999 Natural Resource Challenge, the NPS implemented a strategy to institutionalize natural resource inventory and monitoring. The effort was undertaken to ensure that the more than 270 park units with significant natural resources possess the information needed for effective, science-based resource management decision-making. The national strategy consists of a framework having three major components: 1) completion of basic resource inventories upon which monitoring efforts can be based; 2) creation of experimental prototype monitoring programs to evaluate alternative monitoring designs and strategies; and 3) implementation of ecological monitoring in all parks with significant natural resources.