Shadowsocks is a free and open-source encryption protocol project, widely used in China to circumvent Internet censorship.

[9] Unlike an SSH tunnel, Shadowsocks can also proxy User Datagram Protocol (UDP) traffic.

On 22 August 2015, "clowwindy" announced in a GitHub thread that they had been contacted by the police and could no longer maintain the project.

[17][18] Other server implementations include one in Go, Rust, and C using the libev event loop library; C++ with a Qt GUI; and Perl.

There are also client-only implementations available for Windows (shadowsocks-win), macOS (ShadowsocksX-NG), Android (shadowsocks-android), and iOS (Wingy).

[23] ShadowsocksR is a fork of the original Shadowsocks project, claimed to be superior in terms of security and stability.