The concepts, methods and procedures for describing rangelands help define the profession of range management. None of these is more important than the system for dividing rangelands into spatially distinct units for the purpose of classifying and managing. Range Sites and Range Condition and the ecological concepts on which they were based dominated research, policy and application virtually from the time SRM was formed (1948) until the late 1990s. In 1997, the revised version of the NRCS Range and Pasture Handbook first referred to Ecological Site Descriptions (ESDs) and gave basic guidance on definitions and procedures for implementation. The change from Range Sites to Ecological Sites is representative of two important changes in the profession: the incorporation of nonequilibrium ecology to describe rangeland dynamics in some ecosystems and the expansion of the array of ecosystem services provided by all rangelands.