The country has identified health information exchange (HIE) as an essential strategy to address our crisis of cost, quality, and safety in health care. The Nationwide Health Information Network (NHIN) will consist of a "network of networks"--interconnected local or regional HIEs. We must create policy and technical interfaces that allow these local exchanges to share data with each other. More importantly, we must create nationwide exchanges that are consistent across the country. The should be parsimonious--not overly constraining how the exchanges operate and maintaining separation between the applications that provide functionality and the network that supports HIE.