The Apache HTTP Server ( ə-PATCH-ee) is a free and open-source cross-platform web server software, released under the terms of Apache License 2.0. Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation.

The vast majority of Apache HTTP Server instances run on a Linux distribution, but current versions also run on Microsoft Windows, OpenVMS, and a wide variety of Unix-like systems. Past versions also ran on NetWare, OS/2 and other operating systems, including ports to mainframes.

Originally based on the NCSA HTTPd server, development of Apache began in early 1995 after work on the NCSA code stalled. Apache played a key role in the initial growth of the World Wide Web, quickly overtaking NCSA HTTPd as the dominant HTTP server. In 2009, it became the first web server software to serve more than 100 million websites.

As of March 2022, Netcraft estimated that Apache served 23.04% of the million busiest websites, while Nginx served 22.01%. Cloudflare at 19.53% and Microsoft Internet Information Services at 5.78% rounded out the top four. For some of Netcraft's other stats Nginx is ahead of Apache. According to W3Techs review of all web sites in June 2022 Apache was ranked second at 31.4% and Nginx first at 33.6%, with Cloudflare Server third at 21.6%.