Virtual private networks, or VPNs, extend the reach of LANs without requiring owned or leased private lines. Companies can use VPNs to provide remote and mobile users with network access, connect geographically separated branches into a unified network and enable the remote use of applications that rely on internal servers. VPNs can use one or both of two mechanisms. One is to use private circuits leased from a trusted communications provider: alone, this is called a trusted VPN. The other is to send encrypted traffic over the public Internet: alone, this is called a secure VPN. Using a secure VPN over a trusted VPN is called a hybrid VPN. Combining two kinds of secure VPN into one gateway, for instance IPsec and Secure Sockets Layer (SSL), is also called a hybrid VPN.

Over the years, implementations of trusted VPNs have moved from raw private circuits leased from telecommunications vendors to private IP network circuits leased from Internet providers. The major technologies used for implementing trusted VPNs over IP networks are ATM circuits, frame-relay circuits and Multiprotocol Label Switching (MPLS).