Ecological site descriptions (ESDs) have been characterized as the world’ s largest land management framework. They comprise a database and document collection used throughout the United States to provide management guidance in rangelands and, increasingly, in forests, wetlands, and croplands. ESDs are specific to fine-grained (1:12,000) land classes called ecological sites that differ in soil, landscape position, or climate, and therefore in potential plant communities. Different ecological sites call for differences in the details of management actions such as stocking rates, restoration seed mixes, and strategies for managing woody plants.  The focus of ESDs is on vegetation and soils as primary elements governing ecosystem services including forage for livestock, erosion control, and wildlife habitat. A core part of ESDs is the state-and-transition model (STM) that describes how vegetation responds to management and natural processes. STMs replace older “range succession” models that represented vegetation change as reversible linear trajectories driven by grazing and weather. The STM format encourages inclusion of a broader array of drivers, interactions among drivers, and multiple possible trajectories, reflecting recent advances in ecological science.