The original role of the Internet was to serve as the network of networks belonging to the navy, air force and army of the United States. Subsequently,it was used a path to transmit and access research information. When the Internet opened to the general public, businesses started to use it in addition to traditional print, radio and television media to promote themselves.

　Then enterprises realized that the Internet could act a cheaper and convenient alternative to corporate-built wide area networks(WAN)[1]. The intranet[2] was born. It gave a firm's users at remote sites authorized access to restricted corporate information stored in servers at the main office, via an Internet link. This intranet function has now been elevated to a level where one firm's staff is given privileged access to another corporation's information base. This is the extranet[3].

　As it has to be a secured network between organizations, security is paramount[4]. There is an authorised employee of your partner orgnisation. Authentication procedures ensure this so that data confidentiality and integrity can be maintained.

　While extranets and intranets have a lot in common, the main difference between the two is that in the case of extranets, some parties using the system are out of the enterprise's control. This increases the complexity of administration and integration.