Education Commission of the States (ECS) researched Statewide Longitudinal Data Systems (SLDS) policies in all states, the District of Columbia and Puerto Rico to provide this comprehensive resource. Data dictionaries provide standardized names, codes, definitions and attributes of data elements collected in a data system. In this resource, ECS classifies a state as having a data dictionary if a data dictionary, system user guide or data manual containing such data elements is publicly available on the SLDS or state education agency website. Some states may have data dictionaries that are only internally available to staff or researchers. The data herein indicates whether or not each state's SLDS includes a publicly available data dictionary, and if yes, its location.