This document provides an overview of virtual private networks (VPNs). It defines a VPN as a private network overlaid on top of the public Internet that allows for confidential communications. VPNs apply networking technologies to share a single physical network infrastructure among various logical private networks. They offer benefits like ubiquitous coverage, lower costs through economies of scale, and security through cryptographic technologies. The document discusses VPN products, services, technologies, solutions, vendors and types like site-to-site and remote access VPNs. It also notes barriers to VPN adoption like lack of interoperability and quality of service standards.