The Apache HTTP Server is a free and open-source cross-platform web server, released under the terms of Apache License 2.0. It is developed and maintained by a 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 2025^[update], Netcraft estimated that Apache served 17.83% of the million busiest websites, with the other top four being Cloudflare at 22.99%, Nginx at 20.11%, and Microsoft Internet Information Services at 4.16%. According to W3Techs' review of all web sites, in April 2025 Apache was ranked second at 26.4% and Nginx first at 33.8%, with Cloudflare Server third at 23.5%.

According to The Apache Software Foundation, its name was chosen "from respect for the various Native American nations collectively referred to as Apache, well-known for their superior skills in warfare strategy and their inexhaustible endurance". This was in a context in which it seemed that the open internet—based on free exchange of open source code—appeared to be soon subjected to a kind of conquer by proprietary software vendor Microsoft; Apache co-creator Brian Behlendorf—originator of the name—saw his effort somewhat parallel that of Geronimo, Chief of the last of the free Apache peoples. But it conceded that the name "also makes a cute pun on 'a patchy web server'—a server made from a series of patches".

Other sources also claim that that the name originated as a pun on 'patchy', including the project's official documentation in 1995, which stated: "Apache is a cute name which stuck. It was based on some existing code and a series of software patches, a pun on 'A PAtCHy' server." This documentation did not mention Native American tribes in the context of the name.

But in an April 2000 interview, Behlendorf asserted that the origins of Apache were not a pun, stating:

The name literally came out of the blue. I wish I could say that it was something fantastic, but it was out of the blue. I put it on a page and then a few months later when this project started, I pointed people to this page and said: "Hey, what do you think of that idea?" ... Someone said they liked the name and that it was a really good pun. And I was like, "A pun? What do you mean?" He said, "Well, we're building a server out of a bunch of software patches, right? So it's a patchy Web server." I went, "Oh, all right." ... When I thought of the name, no. It just sort of connoted: "Take no prisoners. Be kind of aggressive and kick some ass."