We developed a hierarchical classification system and map for stream and river systems in the Appalachian Landscape Conservation Cooperative region encompassing parts of 17 states. The product is intended to complement state-based stream classifications by unifying them into a single consistent system that represents the region’s natural flowing-water aquatic habitats. The results may be used to understand ecological flow relationships and inform conservation planning for aquatic biodiversity in the region. The classification used six primary attributes to define stream habitats: size, gradient, temperature, hydrology, buffering capacity, and confinement. These variables were identified and agreed upon by a steering committee of stream and river experts representing the states and region. All mapped stream reaches (1:100,000) were tagged with information on each variable based on extensive data compiled, or modeled, for each reach. For each variable, ecologically meaningful class break