Electronic data interchange (EDI) is used to transfer business messages between two systems. There are many such messages, but the most common are used to support customers sending a purchase order message to a vendor, or vendors sending an invoice message to a customer. In most cases, EDI replaces paper copies of these documents. There are many standards for these messages. In the United States, the ANSI X.12 standard is most prevalent. In Europe, the UN/EDIFACT standard is used, or industry-specific standards are used.