AS2 (Applicability Statement 2) is a protocol for transmitting structured business-to-business data securely and reliably over the internet. It is an HTTP-based protocol that enables the safe, cheap, and quick transmission of messages, especially EDI messages. AS2 creates an "envelope" for the EDI data, allowing it to be sent securely over the internet using digital certificates and encryption.

AS2 was created in 2002 by the IETF to replace AS1, which was created in the early 1990s. It is based on HTTP and S/MIME and uses the same signing, encryption, and MDN conventions used in the original AS1 protocol. AS2 is specified in RFC 4130.

To establish an AS2 connection, two computers, a server, and a client are needed, both connecting to the internet via a point-to-point connection. AS2 certificates are important because they enable secure data exchange and meet certain security standards. Self-signed certificates can cause security warnings and disrupt the exchange of EDI messages.

AS2 provides additional benefits for businesses looking to share point-to-point payloads over the internet, including reduced costs, expanded use cases, and fewer manual tasks. Many household-name, enterprise-level retailers have adopted the AS2 protocol as a standard business practice due to its immensely beneficial capabilities.