AS4 is a communication protocol that has been designed specifically to facilitate the exchange of business data over the internet. AS4 is HTTP-based, with messages sent over AS4 having a specific format which is handled by AS4 software. Both successful and unsuccessful message transfers receive a receipt allowing the sender to know if the transfer has succeeded.

Can be used by any organisation that wants to send and receive documents electronically in safe, secure and encrypted transmissions. In particular, suppliers in the public sector and Peppol network as Peppol only supports AS4 now. Increasingly used in markets that use a service-oriented architecture for B2B messaging, for example utilities, retail and health sectors. AS4 can be a replacement for customers that currently uses AS2/SFTP/FTP clients.