An extranet is a website that allows controlled access to partners, vendors and suppliers or an authorized set of customers - normally to a subset of the information accessible from an organization's intranet. An extranet is similar to a DMZ in that it provides access to needed services for authorised parties, without granting access to an organization's entire network.

Historically the term was occasionally also used in the sense of two organisations sharing their internal networks over a VPN

Enterprise applications

During the late 1990s and early 2000s, several industries started to use the term 'extranet' to describe centralized repositories of shared data (and supporting applications) made accessible via the web only to authorized members of particular work groups - for example, geographically dispersed, multi-company project teams. Some applications are offered on a software as a service (SaaS) basis.

For example, in the construction industry, project teams may access a project extranet to share drawings, photographs and documents, and use online applications to mark-up and make comments and to manage and report on project-related communications. In 2003 in the United Kingdom, several of the leading vendors formed the Network for Construction Collaboration Technology Providers (NCCTP) to promote the technologies and to establish data exchange standards between the different data systems. The same type of construction-focused technologies have also been developed in the United States, Australia and mainland Europe.