An intranet is a private computer network that uses Internet technologies to securely share any part of an organization's information or operational systems with its employees. An intranet can be understood as a private version of the Internet, or as a private extension of the Internet confined to an organization. An organization's intranet does not necessarily have to provide access to the Internet. When such access is provided it is usually through a network gateway with a firewall, shielding the intranet from unauthorized external access. The gateway often also implements user authentication, encryption of messages, and often virtual private network (VPN) connectivity for off-site employees to access company information, computing resources and internal communications.

Intranets differ from extranets in that the former are generally restricted to employees of the organization while extranets may also be accessed by customers, suppliers, or other approved parties.[1] Extranets extend a private network onto the Internet with special provisions for access, authorization and authentication.

When part of an intranet is made accessible to customers and others outside the business, that part becomes part of an extranet. Businesses can send private messages through the public network, using special encryption/decryption and other security safeguards to connect one part of their intranet to another.