The key financial transactions in U.S. healthcare occur when the provider sends a claim to the payer and the payer adjudicates the claim. This chapter first explains the history of electronic data interchange (EDI) and then shows the powerful, costsaving impact that it can have on healthcare. One bottleneck to EDI in healthcare has been the lack of standardization. This problem was addressed with a law passed in 1996, with which the healthcare industry was still grappling a decade later. The standardization of these transactions will be explored in detail in this chapter. After that, a different aspect of provider-payer transactions is examined, namely, the temptation to cheat and the role of software in combating fraud.