The Apache HTTP Server, commonly referred to as Apache, is web server software notable for playing a key role in the initial growth of the World Wide Web. In 2009 it became the first web server software to surpass the 100 million website milestone. Apache was the first viable alternative to the Netscape Communications Corporation web server, and since has evolved to dominate other web servers in terms of functionality and performance. Typically Apache is run on a Unix-like operating system.

The Apache web server, more popular as simply Apache, represents an open-source web server platform lying in the basis of most of the websites we see today on the World Wide Web. Looking back at the time when it was introduced in mid 90's and gradually adopted as a preferred server platform on the web, we could state that Apache acted as the main driving force behind today's web expansion. As a web server ‘pioneer', Apache has turned into a standard for the development of other successful web server platforms.

Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation. The application is available for a wide variety of operating systems, including Unix, FreeBSD, Linux, Solaris, Novell NetWare, Mac OS X, Microsoft Windows and others. Released under the Apache License, Apache is open-source software.

Since April 1996 Apache has been the most popular HTTP server software in use. As of March 2012 Apache was estimated to serve 57.46% of all active websites and 65.24% of the top servers across all domains.

According to the FAQ in the Apache project website, the name Apache was chosen out of respect to the Native American tribe Apache and its superior skills in warfare and strategy. The website also explains the popular but erroneous origin of the name, A Patchy Server (since it was a conjunction of software patches).

Apache provides a variety of Multiprocessing Modules (MPMs) which allow Apache to run in a process-based, hybrid (process and thread) or event-hybrid mode, to better match the demands of each particular infrastructure. This implies that the choice of correct MPM and the correct configuration is important. Where compromises in performance need to be made, the design of Apache is to reduce latency and increase throughput, relative to simply handling more requests, thus ensuring consistent and reliable processing of requests within reasonable time-frames.

Some of the capabilities supported by the server include support for CGI (Common Gateway Interface) and SSI (Server Side Includes), URL redirection, automatic directory listings, user authentication, anonymous user accessibly, loading modules support, HTTP header metafiles, proxy caching abilities, etc.

These are the reasons why apache server is used for web hosting and this is called apache web hosting.