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. States create their SLDS through a variety of means. The main methods examined in this 50-State Comparison are: statute/legislation, executive order, Memorandums of Understanding (MOUs) between agencies and federal SLDS grants. ECS attempted to identify the primary method of establishment. However, in some cases, states created their data systems using more than one of these approaches. In other cases, state agencies had been sharing data informally even before one of these methods was used.