In the context of the EMR, it is important to understand how existing data systems differ from newly emerging systems, and how existing systems were able to overcome many of the challenges facing those who will be engaged in EMR aggregation efforts. This paper, written by the National Association of Health Data Organizations (NAHDO) for the Agency for Healthcare Research and Quality (AHRQ), will provide an overview of statewide hospital discharge data systems, and the implementation lessons learned over the past 25 years, as well as a call for hybrid data systems combining EMR data with discharge data.