NGINX, stylised as Nginx or nginx or NginX, is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache. The software was created by Igor Sysoev and publicly released in 2004. NGINX is free and open-source software, released under the terms of the 2-clause BSD license. A large fraction of web servers use NGINX, often as a load balancer.

A company of the same name was founded in 2011 to provide support and Nginx Plus paid software. In March 2019, the company was acquired by F5 Networks for $670 million.

As of February 2020, Netcraft estimated Nginx served 36.48 percent of all active websites ranked, ranking it first, above Apache at 24.51 percent, while according to W3Techs, Apache is ranked first at 40.1 percent and Nginx second at 31.8 percent.