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. For purposes of this 50-State Comparison, an SLDS is defined as one with formal connections across two or more of the four core agencies (early learning, K-12, postsecondary and workforce). If a state data system only contains one type of data (e.g., only K-12 data), the state is not designated as having established an SLDS. States including at least two of these core agencies in their data systems are designated as having established an SLDS. As such, the data systems that meet this definition might not always be those systems associated with the federal SLDS Grant Program. If a state's SLDS is still in development, the state is not designated as having established an SLDS. However, ECS made its best efforts to identify such states and designate them as being in the process of establishing an SLDS.