Education Commission of the States (ECS) researched Statewide Longitudinal Data Systems (LSDS) policies in all states, the District of Columbia and Puerto Rico to provide this comprehensive resource. ECS identified two main approaches states use to connect their data: centralized systems and federated systems. State data systems that collect, retain and maintain data from multiple agencies in a centralized warehouse are designated as centralized systems and state data systems where data from participating agencies was linked temporarily or on an as-needed basis are federated systems. This resource indicates how each state's data connections are structured.