Definition
A VPN client is the application that runs on a user's device and handles the user-side half of a VPN connection. Its responsibilities include initiating the handshake with the server, authenticating credentials, negotiating cipher suites, encrypting outgoing packets, decrypting incoming ones, and inserting itself into the operating system's routing table so traffic flows through the tunnel. Some clients also provide a graphical interface, server selection, kill switch, and other quality-of-life features.
Categories of Clients
Provider-branded clients are the apps shipped by commercial VPN services — they bundle protocol logic with account management, server lists, and convenience features. Open-source clients (OpenVPN community client, wg-quick for WireGuard, strongSwan for IKEv2) implement the protocols without provider-specific extras and are auditable. Operating system native clients (Windows, macOS, iOS, Android) handle IKEv2 and L2TP/IPSec out of the box. Headless clients run on routers, NAS devices, and servers without a graphical interface.
Trust Considerations
A closed-source provider client is harder to audit than an open-source one. Privacy-focused users sometimes prefer to use the underlying open-source protocol clients with the provider's configuration files, accepting fewer features in exchange for full transparency. Most reputable providers now publish open-source clients or have them externally audited.